A friend just bought an older high hour full size backhoe for $12K. It is 2wd, with good engine and the manual transmission. It needed attention everywhere and tires + a battery & lights just to get it home. Steering was an adventure and the brakes didn't work. But it basically ran and everything worked after a fashion even if everything needed work. Over the last few years he has worked with it maybe twice as much as much as he has worked on it. Everything important is finally done and now is in better shape now than when he got it. My guess is that he has put another ten grand into it. But he is a master mechanic and enjoys that sort of thing.
Now he has a machine he feels comfortable keeping as his "forever tractor", and he did it with money he could afford.
Looking back on his project, I think this worked out for him because it had a good engine, transmission, and decent hydraulics. He and I could run it enough to tell that none of that stuff was broken, although every single control, switch, and lever needed a rebuild. And even more important, all the parts are available everywhere for that old JD backhoe.
So I guess I am saying that I agree with what you want to do and I've both seen it done and done it myself. Your price seems ballpark OK. You aren't alone; lots of guys have done the same thing. Fixing up something old used to be a common way to get started in life. If you do that with a tractor, and then a car and finally a house, you end up way ahead. So the idea is good, but the critical thing is... is this the right tractor to start with? I'm assuming you are after a keeper....
Sometimes making up some rules help me make a decision. It might help you. I'd suggest that if the motor bottom end is strong & no leaks.... and the probablility is high that it just needs injectors and maybe a valve job I'd say it is a "yes" for that, but only if the transmission and rear end are good too.
You've got enough downsides especially with rusty rims and bum tires that you have got to also have some upside. With the one my buddy bought, once he got it home he was able to do a month's worth of small projects with it even though it needed just about everything. In my buddy's case,
So if that motor seems sound, you are looking at injector rebuilds and a head job that will run you in the neighborhood of $1500 instead of $7500. Now all of a sudden the project makes sense. I expect you are the type of mechanic who will rebuild your own starter, alternator, clean the radiator up, and replace steering spindle bushings or hydraulic seals at home on your shop work bench - or at least one who doesn't mind learning how. This kind of project takes that. In the end, enjoying the work makes all the difference in the project.
rScotty