Ok here it goes.(This is not exacty like uncharted waters but is the economy I would like to implement.)
1:Every city has trade goods at varying prices.
2:Each city has production rates for the various goods.
3:When you purchase goods the price goes up because you're buying out stock.(Only at the town of purchase.)
4:When you sell goods the price of selling that item goes down.(Same as 3.)
5:There is random shortages and overflows of goods.
6:Items are priced differently in each town.
7:Every city has specialty items which can only be bought there.

The parts I have not been able to figure out are random shortages and overflows,and the changing of price dependent on how much of it you bought or sold.I also cannot figure out the production rates.