I really like some aspects of the kingdom building rules in Kingmaker but hate the magic item economy and with the help of some other 3rd party rules have been creating some alternatives. This is an outline of what I've been doing.
Each 12 mile hex can have one settlement and each hex has four natural resources.
The Kingmaker 3x3 city grid is a good way to represent a city and its buildings, but for me I changed the population per square from 250 to 100. Each square can have up to 4 buildings (as per kingmaker rules) but also, each populated square represents 1 unit of Human Resources.
A human resource unit can be allocated to work a natural resouce, build improvements, be the watch, patrol roads or be the army.
The basic economic considers that a natural resource is extracted, processed and then crafted into a finished product that is then consumed. Taking a single city grid square as a self supporting entity, the population harvests the resource [lets assume it is wheat grain], one building processes it [e.g. a mill turns it to flour], a second building crafts the processed goods [e.g. a baker bakes bread]and a third building consumes it [I've repurposed houses as this building, but contradict this example with food later]. The fourth building square can then be used for something else, such as a chapel or an inn. Each building can convert or consume 1 unit per month.
Back to resources - a natural resource may be worked to produce more than one unit, in fact this is necessary to enable things other than food to be produced. For my purposes I divided the resources up into Common, Uncommon, Rare and Very Rare and then gave an abundancy for each resource ranging from 1 to 5 units per month. With common items being more abundant than rare items. The resulting tables are then balanced so that 1 unit of human resources produces on average 300GP worth of natural resources. 300GP is based on 100 workers earning 3GP, enough to live a poor lifestyle. The cost of the natural resource can then be worked out (I don't have my notes with me unfortunately) but say the average for common goods was for 3 trade units to be produced per month then the cost of a trade unit of common raw materials would be 100GP.
I consider the average craftsmen to live an average lifestyle, 10GP per month. According to the craft skill 1/3 of the cost of a finished good is the raw materials, assuming no wasted material. This would mean to earn 10GP he would need to to buy 5GP of processed material and sell it at 15GP. Now the labourer who gathered the raw material has sold it for 3GP to be processed. The labourer doing the processing should also earn at least 3GP, so the processed materials cost the craftsman 6GP instead of 5GP. This extra GP can be assumed to be material wastage but the price is added to the cost of the finished goods, which are now 16GP not 15GP, but to keep things simple on a macro scale a striaght x3 multiplier of the raw material cost is simpler, so the goods are worth 18GP. Scaling the individual income out into trade units, our 100GP common raw material was processed into 200GP worth of grain and became 600GP worth of bread.
Each city grid square required 1 unit of food per month so a house isn't required to consume it. This frees up houses and similar buidings to consume non food goods (this was my earlier contradiction with hosues and food).
With this model, small settlements - up to 4 city grid squares - will be able to work the land and produce a raw material surplus but they won't have the building space to process and craft all that they produce. Larger settlements will be able to convert resources but won't be able to support themselves.
Building materials and human resources would be required to build additional buildings.
Other finished items would be required to keep the population happy. More on this later .
Goods tend to travel from small settlements to larger settlements. So a group of settlements are expected to form around a city. To simplify things a city and it's surrounding settlements should be considered one entity to work out the overall supply and demand of goods. This sets the market price as opposed to the base price. Again I don't have my notes so forget the formulae used to stimulate prices.
Cities within two week's travel may trade [two week's allows travel there and back in one month]. Merchant shops and similar buildings (as opposed to craftsmen) are required to import goods from neighbouring cities. If a neighbouring city has a good then a demand for 1 unit is created in the city.
As well as supply and demand, trade is affected by the capacity of the roads and the safety of the road. E.g. a track could carry 10 units a month, a road 100 and a highway 1000. Similarly water travel could be accommodated with a wharf, jetties and a port coping with 10, 100 and a 1000 units per month. Each hex has a safety rating based on the settlement size, frequency of patrol and area safety, which declined thre further away from the city (and civilisation) a hex became. The profitability of the trade multiplied by the risk factor gave a likelhood of the trade happening.
Taxation can be set against any of the income and this is what is earned, produced resources are spent feeding the population, creating and maintaing buildings and supplying the watch and army. The rest of the produced goods are consumed by houses. Unless a good is consumed or exported it cannot be taxed.
The lower classes would be unhappy if there was a food shortage and if there was a loss of control then the human resources would not be available.
The middle classes would always be able to get food but would be unhappy based on taxation and if there was a loss of control the buildings would stop working.
The upper classes would always be able to get food and pay tax but would be unhappy if they were unable to get the variety of goods and a loss of control would prevent edicts or executive actions from being passed or actioned.
I know it looks like a lot but my eventual aim is to setup a computer program to run every month, which will give a fuller game world without requiring a lot of effort on my behalf.