@adairhammer - I wouldn't remove Negotiate, as it has a place the other social skills don't fill. Sometimes it's just about the hard facts, the numbers, the quality of an item, the truth of what you have to offer. No charm, deception, or intimidation can change those factors, and having to fall back on one of those skills for straight negotiation would be disingenuous.
The biggest issue I have with a wealth system that provides an experience penalty to someone because they're wealthy is that it doesn't even remotely model reality in any sort of world. The wealthy are always better trained and healthier, tend to be smarter, more cunning, more athletic, and have better access to services. In truth, if you wanted to have a wealth system that made sense, the rich should actually start out with an experience bonus, rather than a penalty.
Of course, that's just no fun, and the point of this is fun.
Leaving off any XP bonus or penalty, you could determine wealth by random roll at character creation. Unfortunately, that takes away player agency when it comes to their characters, and any realistic table for rolling would have the vast majority of the players at the lower end of the income spectrum.
The way I would do it is to tie your character's wealth their background. That would mean there would have to be codified backgrounds, each one ranked for wealth, but coming up with five to ten background/wealth ranks shouldn't be too difficult. From there, you have options.
The GM can start everyone with a certain wealth threshold.
The players can be allowed to determine their own.
The second option would, of course, cause variable degrees of buying power within the party, but as long as the players are good with it, that shouldn't be too much of an issue. Of course, that sort of income inequality doesn't suit some players (or some GMs), so it's easy to fall back on Option 1.
So now we have an attribute called "Wealth" that's ranked 1-5 (which, I admit, isn't granular enough for me - I'd rather go with 10 ranks). Your character can make a reasonable amount of purchases within your Wealth strata each day (or each week, or each month, depending on how the GM wants to do it). If you want to overextend yourself, you can do so once per session per point of Presence, but doing so requires a [Social Skill] roll. Which social skill depends on how you want to go through with the purchase. Some sort of table akin to the Alchemy table in Realms of Terrinoth could be created to help determine how Triumphs, Despairs, Advantages, and Threats are spent on such a roll, but it should include possibilities such as...
... on the positive side:
Reduction in the cost of the item.
A net positive outlook from the seller (which may lead to better pricing in the future).
Trading the item for a favor instead of money.
The item being of superior quality (not necessarily having the Superior quality, but being better than expected).
... on the negative side:
An increase in the cost of the item.
A net negative outlook from the seller (which may lead to worse pricing in the future).
The item being of inferior quality.
Temporary loss of Wealth ranks.
Permanent loss of Wealth ranks.
I'd leave off the bean counting completely, but instead create modifiers for rolls, similar to how the Star Wars economy had different adjustments for different types of worlds. That way, a black market item might end up costing a little more, or an item that's got a high rarity might be a little more expensive (while super-low rarities might drop the value of an item).
Treasure or loot could then be used to increase a player's net wealth. There would have to be some sort of algorithm to determine how that happened, and it would have to scale up all five or ten ranks you include in your game. It shouldn't be easy to reach the top three or four tiers of wealth for someone who started low, nor should it be easy for someone who started high to lose it all just by making purchases.