Well... uh, "ready to fall apart" and "way to save it" just don't go together. If the frame is rusted through it could be disconcerting to drop a rear quarter panel while making a fast curve. On the other hand, I have driven cruisers til they brake and always made it home.
Find a mechanic you trust. If you don't know one, go to the LSLC meeting at Rudy's BBQ the last Thursday of each month. That's Rudy's in North Austin (183) at 7pm. Folks will help you find someone. Next, tell your mechanic what you plan to do with this beast. Driving cross country is very different from rock crawling.
As for how much, remember this: ...a bit now means a lot less later. Your FJ62 will never be young and new (unless you want to spend a fortune). So, make sure it's sound and trustworthy. Again, the guys & gals with Lone Star will be happy to help.
If you want to talk about specific issues, you'll find my number on the inside cover of Toyota Trails. HTH
Happy Trails! N