If it is in daily driver, #3, type shape, I would say about $4000 is around the most I would be willing to pay for it (unless the bug to buy just bit me).
Of course, there are a lot of factors to think about. If the quarters are bad, they may cost quite a bit to replace. Bodywork in general is expensive.
The 6 cylinder cars don't necessarily gain too much value by being numbers matching. In fact, I would venture to say that most people would pay more if you took out the 6 and put in a V8 unless you want to make it a concours show car.
If the car you are buying is in Tennessee I would say that it could be had for less. Prices are very dependant on region. Here in Northern Va (in close to DC) First Gens will run a pretty penny, but if you just go a few miles out you can find one in the same shape for 1-2 thousand less.
If you really like the car, you think the price is right, and you are willing to pay for future work should you decide to do any... then I would say go ahead and get it and have fun.