Well by about mid game, the cost of items is no longer an issue.
- NPC's restock every few hours of gameplay, and on top of lvl ups.
- Using a barter henchman, you can buy/sell at the same price.
- You can make unlimited money buying up crafting mats, and selling finished goods
- Certain npc's will almost always stock legendaries, giving you a big incentive to resolve their quests in ways they don't die, or to leave their quest unresolved, so you get more sources of legendaries.
I don't know what a good economy would be, but it's quite easy to game the current one. After you get out of Cyseal, money is no longer an issue for anything really.
