There are many factors.
There you have it, a supra for 10,500. And you complain that its f**ked? Of course its gonna be crap.
I looked at almost 10 supras before actually deciding. You have to be patient before finding something good, and in my case, it was not a bad buy, but it was dusty as f**k and having cracked sideskirts/slightly faded paint etc, and on the day i took ownership of the car, i spent the next 4 hours cleaning up dust, and grime that had accumulated over the years, although the engine bay was mint. Its weird eh, but when i saw the car, i just wanted it. Automatic or not, didn't matter, i'm a lazy boy anyway.
So, my advice to you is, to be patient, and look around, skylines are cheap for about 12grand you can get a nice 33gtst, but you should never be hasty. Take your time.