The bike I have been looking at is now in my price range and I need your opinions before I pull the trigger

It's an '87, not in the best condition, with corrosion on the engine covers. There may be a spot of rust or so on the front shocks.
I asked the owner if it leaked/burned oil. He said only after it was hot out some breather tube. He also said "it doesn't burn oil unless you ride it 75mph and then it gets hot and burns oil, but that is normal". Come on, that can't be so???
He'll take $700. Is this just fine, knowing I'll have to put in another $800 or so?
Or is this not fine? Just realize that I want to restore the thing and repaint. I do not mind the work. I do not want to spend more than an additional $800-$900. I am mechanically inclined, although have never had one of these engines apart. I can do the painting myself.
I am concerned about any rust on the front shocks. I know little about shocks. I don't know if I can repair this, replace parts myself, or if this is strictly for someone with the proper tools.
Am I wasting my time with such an old bike?
Tom