Fork it?

I'm putting the cart before the horse a little bit here, but I keep asking myself: When should I take it out back and put a bullet in it? At what point (dollar-wise) should I give up and sell the GTX off? I'd rather stick to it keep it running. I can see having this as a project car, slowly working on items myself, and I'd enjoy working on it, but I know little about working on cars, and have few tools to do it with. I am planning on doing the little, easy things like replacing a headlight, replaceing the hatchback struts and fixing the dome light. But there are easy sounding this I might shy away from like replacing the steering wheel (because of the airbag). This isn't even getting into the harder problems like the 4WD system not engaging or the suspension getting old.


So, when do I cut bait, when do I stick a fork in it, as it's done?