Characters start with 0 wealth.

When a player acquires a small bag of coin, coin-sized gem, or similar, they get 1 wealth.

When the player acquires a large bag of coin, a large gem, or similar, they get 2 wealth.

When the player acquires something uniquely valuable they get 4 wealth.

When a player wants to buy something, tell them the cost. They subtract the cost from their wealth and roll that many + 2 dice, total the two highest. On a 10+ they get it at a good price: reduce their wealth by cost-2. On a 7-9 they get it at the cost you stated, -cost wealth. On a 6- it comes with strings attached, if at all.

Why wealth+2 dice? I get that you want characters to be able to barter or trade for items at wealth 0 but it seems like a bit of a gimme after that.