It's been made pretty clear from the designers and from people on the boards that there is no direct correlation between BP and GP.
However, it has been made equally clear that many people find the idea that 2000GP 'buys' 1 BP to give an implied value to BP, or at least that they feel their players are not going to buy into the idea that 1 BP does not have a 2000gp value.
So, I was giving it though, and came up with the explanation that I am going to use with my players that I believe they will be able to accept without breaking immersion: waste and premiums.
In raw, hard currency, 1 BP has a value of equal to perhaps 200GP (this figure is not set in stone, I'm sure those more interested in doing the math can come up with a figure that feels right considering army upkeep costs and such). The extra cost represents the waste and additional expense of pushing a kingdom's economy beyond its normal capacity.
Need an extra BP to finish a building? It costs 2000gp to import extra temporary workers beyond the available labor force, to import materials beyond what the current economy produces, to pay additional costs for overworking current population, and to generally offset the damage done to the kingdom's economy by running it 'hotter' than it is currently designed. The value you get out of it is far less than 2000gp, but you are paying for speed.
This also opens up the possibility of events or structures that influence this wastage cost. Perhaps a Caravanserai that increases the flow of goods, or a Labor Hall that increases the available workforce, either of which could reduce the cost of 'buying' a BP by 10 or 25%.
An Event of a glut in labor materials or sudden influx of refugees could present rulers with a choice: Buy 4 BP at 75% of the normal rate (in order to absorb the influx into the economy and make use of it), or suffer a -2 to Economy (for a materials glut) or a +1 Unrest (for a labor glut). These numbers likely need tweaking for balance, as this just popped into my head, but I think the idea is sound, and it can present a real concern if it hits when party funds are low or they've just spent all of their cash to hurry building, only to find that a sudden change in available materials requires that much more of an expenditure.
Similarly, an Event of a sudden Labor or materials shortage could result in increased costs for additional BP until the next Event Phase.
Thoughts?
Generally gp going into the treasury converts at 4,000 gp per 1 BP.
Note that there is an Unrest penalty for withdrawing from the treasury into gp: 1 Unrest per BP converted into cash.
A big part of the reason is that, for the untrained laborer, that much money represents the entire labor value of about 110 men for a year.
For professionals - earning about 1 gp per day as a reasonable base line - that's the gross income of 67 families for an entire month.
I can see why the masses might get a wee bit upset about this. :)
Waste / corruption seems to have already been built into the consumption costs derived from the sheer size of the kingdom as well as the total number of city districts from all of the kingdom's cities combined. There is only one way to reduce this cost without relying too heavily on a very robust - and thus relatively fragile - economy: farmlands, and lots of them.
A fully-developed city of 9 districts has a consumption cost of 10 (1 hex +9 districts) per month, not accounting for edicts. You probably won't see a kingdom smaller than size 11 able to self-sufficiently afford one fully-developed city/town.
Consumption cost per month, not accounting for edicts: 0, with 10 farmlands & roads. (11 size +9 districts -20 farmlands)
Size 11 = Control / Command DC of 31. This is easy enough to deal with I would think in most campaigns.
Granted, it is also unlikely that the Barony could have afforded to fully develop all 9 districts - just that it is possible, at least in theory.
My error...4000gp/BP, not 2000. The question is, is this sort of explanation likely to alleviate player immersion concerns about BP/GP 'conversion'?
I had some problems understanding BPs and the sale of items. In the Rivers Run Red thread, Jason Nelson explained it very well. He explained that BPs do not equal GP.
Jason Nelson wrote:
BPs also represent not only material resources but also productive activity. Take the example above. Rex is going back and forth between East City and West City as a go-between. Some of his business exists in between the cracks of the system (i.e., hundreds of penny-ante transactions that don't show up by themselves on any BP ledger sheet), but he and a dozen other merchants just like him are plying the roads and marketplaces of your kingdom working the low-grade item trade. They also are information brokers, making business connections. Think of them as headhunters, making a profession out of connecting potential buyers with potential sellers.
They are spending dough working the inns and markets looking for customers and clients. The inns and markets profit, because they're throwing money around on rounds of drinks and food and rooms for themselves and their guards (essentially, advertising). When they actually *DO* find a customer, they work with individual suppliers to connect them. Then merchants get into the picture to transport the goods. Then they hire guards and buy wagons and horses, and those guards need equipment, and now that those guards have equipment they, after they finish their first contract, can find other work with other merchants.
All of this spawned from that wand of bull's strength you rolled up, to get it from point A to point B, there is a teeming hive of economic activity associated with that transaction and implied transactions just like it... that economic activity moves the gears of your society and builds up BP worth of resources.
Now, you could argue it's just money changing hands, and nothing is really getting BUILT. Well, if you must then presume imports of good and services, new settlers attracted by the vibrant economy, foreign traders bringing in new goods and services to try to get in on the action.
The fact that the magic item transaction system relies on specific, discrete, tangible items is the glaring exception to the otherwise nicely abstracted BP system, because it keeps drawing the eye back to the idea of "BP = GP = specific tangible goods." It's not.
Accept the particular items as representative of the general trade that is happening and the BP produced by their "sale" as more an aggregate "economic stimulus that comes from selling these kinds of items, of which this ONE was a particular example."
Hopefully this will give you a better idea.
BP =/= GP. You can't store them in a vault. They aren't cash.
BP = the goods, resources, activity, effort, and output of everybody in your kingdom, from Farmer Frank's ant farm in Hex G-8 to Jennifer's Jewels and Luxury Shop in your capital city.
You (the kingdom rulers) are not selling a physical item (the magic item you rolled up) that belongs to someone else (Diana the wizard in the Caster's Tower on Vine and 2nd Avenue) resulting in cash to you (BP).
Instead:
You (the kingdom rulers) are overseeing and managing the economy of your kingdom, including trade in magic items (such as, the magic item you rolled up) that was created by people are a part of your kingdom (Diana), and their economic activity increases the wealth and success of your kingdom and its people as a whole (BP).
Not sure I would attach any mechanical rules to it beyond 4000 to buy a BP and 2000 from selling a BP. This is pretty much how I describe it though. 1 BP is the ecconomic activity that you get for adding 4K back into the economy and buying labor with it. It is promoting jobs, encouraging more people to come to the area. It allows merchants to buy more from traveling caravans, which in turn encourages more merchants.
And it works the other way too. You can spend that ecconomic activity on a temporary levy and increased taxes. This will shrink your economy by 1 BP and make people unhappy, but will produce 2000gp cash in hand for you.
Excellent explanation of BP and why you don't want to cashier your treasury.
Magic items are likely to become the cornerstone of the economy of most kingdoms - the BP output is phenomenal and the DC 50 Economy check is super-easy to pull off.
It's also how a kingdom can afford armies ^_^.