I don't have any other economic responsibilities, but a $40 phone bill.
Oh, and I make much more than minimum wage at a full-time job, with only a four day week. Oh, and unless my suspension/brakes/tire upgrades fail, no, I shouldn't have to worry about repairs.
Seriously, I don't have to worry about economics. I've been slowly modifying the car with OEM or better parts for about a month now, and my bill (the phone bill) was always paid. And, if worse comes to worse, I can dip into my savings account a small bit. However, even as-is, now, I can afford the best tires on the market, pay for them, and still not have to go without my phone or my savings account.
With that said, I'll have 2 sets of rims, three sets of tires, two sets of springs, two sets of brakes, etc. For "just in case something breaks." Why else would I keep the parts I take off/change?