It depends on what you want to end up with, if you are not to concerned with originality, then a Corvette is no more expensive than any other car (and in the case of the interior much less expensive), but if you are trying to build a stock vehicle, it will get real expensive real quick. One day I plan on getting a mid seventies Vette, but I could carless about it being original.

What do you mean by "repro interior pieces", my opinion with old cars is, you can often find what you are looking for on another car, and use it with very little modification, as far as seats, go, they are not that expensive to have rebuilt using much nicer material than original (whether you are wanting leather, vinyl or cloth), plus with a Corvette you only have the front seats to deal with. The carpeting and headliner are also easy to take care of at local shops. For all of the little widgets and plastic bits, it depends on how original you want it. I used to have an old Volvo 240, which was a real tank, but a few items that it came with from the factory were the epitomy of "Mickey Mouse", like the dome light, mine broke, I located a replacement for $40, I went to the junkyard and found a domelight in a little jap car, that fit perfectly, looked better than the original, and worked better than the original, I jsut had to splice a couple of wires, and the part was only $3.

The repro parts are probably going to be knd of steep as well, at least for true OEM quality. Like I said, if you are not concerned with originality, you can sustomize many parts to work, and if done properly you will end up with a very nice car, if done carelessly will leave you with a raggedy junker. It is all a matter of personel taste, I like Cd players, and that kind of stuff, whereas many feel that a CD player in an older car is blasphemy. A tape measure and the imagination to visualize what you want rather than what is there goes a long way. I have a 74 Maverick I am working on right now, I want several features that not only are not original to the car, but were never available on a Maverick, like power locks ,cruise control, and leather poser seats (maybe even heated), tilt wheel , and some other things that weren't even avaiable in the era that Mavericks were built, like keyless entry, and I have figured out how to add these features in a manner that if you were not aware that they were never available for car, you would assume were factory. Of course I will have used some repro parts, such as window seals, and a few chrome bits, and they were expensive, but not to bad.

With the Corvettes they are very popular to this day, therefore the demans is high enough to keep some of the more popular restoration parts available and inexpensive, but when you start dealing with harder to find parts, the people who have what you need have a tendency to get very proud of thier products, especailly if they are exclusive to a status marquee, liek a Corvette.

Edited to add: of course by the early seventies GM had started to streamline thier parts process, and intercahngeability between makes, had become important to thier business model, and you would be surprised in the difference in the price asked for the same aprt, depending on what body it came of of, in the Ford World I have seen "Mustang" door handles go for twice what the exact handle would cost if taken from an old Ranger.