This would probably depend on how it was driven and maintained. My friends dad had a green one for as long as I've known him. I think it had something like 420km on the dash. But he did take care of it.
It all depends, take a careful look around the car and drive it... you have to see how it feels, if it rattles, if it makes funky unusual noises, how easily it shifts, if it pops out of gear, if the clutch is slipping, and make sure u actually test the car and just just drive it around the block at low revs... If they guy tells you not to do something he's probably hiding something.
how much is he asking for? As for trannies... you should be able to find lots around, and from what I know you dont necessarily have to get the same tranny back in, others should fit that motor too. (dont quote me on this, ask the guys that run shop)