http://www.restorationperformance.com/servlet/the-ALL/keyword/1968+Pontiac+Firebird/Categories
Browse that website to get an idea of how much you just might be spending
The thing is with rusted floor pans and a convertible, there’s not much else holding the car together from front to back. That’s why it would be a parts car. For a restoration of a good candidate though, I think we are into the $20-40,000 category though if everything is hired out. Might want to spend some time at some car shows and talk to the guys to see what they have done. Depending on where you are, the Back to the 50’s in St. Paul is a great place for this.
At best its a parts car. You can buy a new body shell from Goodmark. If I was going to do it thats the way I would go. Its way cheaper, as you start with a new rust free body. Then just take parts from the parts car. Renew parts as nessary. You will sill have about $20,000 -$35,000 in it when done. But when done if you use the right upgrades it will ride better and handel like a new car. Hey would not want to have a better than new 68 FireBird convert. Ckeck out these links http://www.musclecarmetal.com/1968_CAMARO_BODY_SHELL.ASP
http://www.dynacornclassicbodies.com/gm_models2.html