Please dont take this the wrong way, but you need to get someone who knows about cars to personally go with you and check this vehicle out. Pin-hole rust means rust-through. Rust-through generally means 'requires complete replacement'. It also usually means there is more rust but you just cant see it. Camaro's are very prone to rust. I started making a list of most likely places you'll find rust, but the list was getting too long to include in this post. Suffice to say, if you can see pin hole rust on the body, trunk and underbody, and the vehicle was recently painted, there is likely to be a ton of bondo hiding more serious problems.
The aftermarket makes loads of parts for these cars now, but if you dont know how to repair it yourself (weld for example) you'll be paying someone else to do the work for you and it gets expensive fast.
Things like windows not going up and down properly are items that are easily fixed. As are leaking gaskets and rusty engine pieces. But items like replacing floors, trunks, and window channels are not easily fixed by the amateur. And after all that, you'll likely need to repaint the car. That's not cheap or easy either.
My advise to you is two-fold. One, go to your local garage and hire someone to scope out this vehicle for you. Offer to pay him for his time and expertise. (It beats buying an $18k lemon). Two, spend more time researching first gen Camaro's. Learn more about them. Go to CarTraderonline and see what else is available. Check out other sites like camaros.net and camaross.com, both sites have a vehicle for sale section and knowledgeable people. Take your time, dont rush into this. They made a half a million first gen Camaros. It'll be ok if this one gets away.
Bottom line, if this was an original v6 car, it was probably nothing special. IMO it would have to be pretty freakin' sweet to be worth $18k.
If you want, send me an email, firstname.lastname@example.org
, and I'll send you a list of specific things to look for and look at.