You could do what I do for my Audor D&D campaign, and intend to do for MWWG:
Higher level characters do not get any more starting money than lower level characters. If they want more money, they have to spend character points to get it. In my Audor D&D game, one character point can buy 100 gold pieces of starting cash. It seems fair to apply the same rule to MWWG, with one character point buying $10,000 cash (assuming that $100 is equivalent to 1 gold piece in terms of spending power; I haven't decided how to account for inflation -- I'd have to look over the prices to decide).
An option I intend to implement for my World of Greyhawk D&D campaign is to have the players roll for social class. Social class defines a monthly income. The player then rolls for one month's income, and multiplies it by the PC's level and wisdom score.
Hope this helps.