Magic Item Additional Ability Cost

[MerlinRedbead]

Core Rulebook wrote:

The cost to add additional abilities to an item is the same as if the item was not magical, less the value of the original item. Thus, a +1 longsword can be made into a +2 vorpal longsword, with the cost to create it being equal to that of a +2 vorpal sword minus the cost of a +1 longsword.

If the item is one that occupies a specific place on a character's body, the cost of adding any additional ability to that item increases by 50%. For example, if a character adds the power to confer invisibility to her ring of protection +2, the cost of adding this ability is the same as for creating a ring of invisibility multiplied by 1.5.

So let's say I add a cloak of resistance +1 to my muleback cords. That should be as follows (If I'm understanding this correctly):

Muleback: 1000gp
Cloak +1: 1000+500
Total: 2500

Now what would the cost be if I wanted to increase the cloak bonus above to a +2? Would it be the 3k for a +1 to +2 cloak? Or the difference between a muleback+cloak +1 (2500gp) and a muleback+cloak +2 (7000gp)? Would this change if I added muleback to the cloak +1 instead?

[_Ozy_]

The best way to do it is to calculate the new cost of the magic item:

cloak +2:4000 + muleback: 1000 + 500 = 5500

and pay the difference from the old cost.

[dragonhunterq]

In theory the order you add or improve items can affect the cost.
I would recommend adopting a policy of counting the most expensive part of an item as the base and adding 50% of any additional abilities. It means no matter how an item is upgraded or added together you always end up with the same price.

[James Risner]

+1 _Ozy_ / dragonhunterq

(Most expensive feature) + (least expensive feature) * 1.5

[Claxon]

Yeah, the price should always be the same regardless of how it's upgraded.

Always treat the base item as the most expensive item.

When upgrading from a +1 resistance cloak with muleback to +2 you simply calculate what the cost is (5500 gp as calcualted by Ozy) and subtract the value of the old item from it, 2500 gp.

[Ravingdork]

The final cost will always be the same, regardless of order, but yeah, upgrade cost may well vary based on what you start with.