I used my two free lessons today to think about some thinks regarding The Mana World. One of the outcomings was the idea of a dynamic market (like in space-trading games like X - Beyond the Frontier), so that if a bunch of players sell masses of a special product in a city the prices for this special prodcut (or if it is a resource, the products basing on that) will descent bit by bit.
To create a realistic economy situation in the Mana World (so, that a city at the coast sells more and cheap fish and water in a desert cities is rare and expansive) I've got the following idea, which might not be really realistic, but is much simpler to implement that to let npc chipping wood and go fishing (this could be implemented later

It's like that:
What is needed first is to set resource spots on the world map (i.e. "wood" in a the forests, "fish" in the sea, etc.). Then you could calculate the distance of the particular city to those resource spots in the near. On the basis if this distances you could then calculate how much of the appropriate resources and goods basing on those would be on the market - for example would a city near a large wood sell much very cheap things made from wood.
I think this idea is good to create a realistic game world and it furthermore saves time and effort otherwise used to think about and edit all the markets manually.