I am in need for a trading system to create my sailing commerce RPG game.  I need menus to buy goods and sell them in different towns.

Supply and demand affect prices and some goods are only available in some towns.  Some towns exclusively need some or one good.

Can you build this? I would buy it.

Hi! I have a template for a shop menu, but it only works for buying items and not for selling them. You can use it to adjust stock quantities and prices per shop, also.

However you might have a better time using something like VisuStella's Fluctuating Shop Prices plugin. :D