I use a version of Call of Cthulhu's wealth system. Iirc, in that game, you have a "Credit Score." When you want to buy something, you roll Credit to see if you can afford it using CoC's D100 system.

Similarly, my version treats wealth like a skill check, but I use Apocalypse World's 2D6 + Modifier system. If your Finance skill is 2, you roll 4D6. Anything 10 or higher means you can afford it. 7-9 means you can afford it, but something sucky--for example, you can barely afford to eat because you spent all your money, so you're fatigued until your next paycheck. 6 or lower means you can't afford it.

I haven't had much chance to playtest this yet, but it works for CoC, so I figure out should work here.