Bob speaks sound advice. All of us who have started with a fixer upper will tell you the more it needs fixing, the way more it's gonna cost in the long run. With the economy the way it is, biding your time and saving up maybe for a 3k car, might get you one in driveable condition. Even driveables cost alot to fix up down the line, but if your starting with just a frame, yikes it will cost 3x's what you would have to put into it, to buy one already in the shape for what you spent. Now if you know this, and want a project to work on for a few years with the kids, realizing it will cost more over time than an initial outlying of cash to begin with, then welcome to the club many of us have joined.
I love the early 70's muscle cars. I believe there is a big aftermarket for most of the parts, including sheet metal, but if it's like what I'm paying to replace a few fenders and running boards on my truck, you might want one with a good skin on it. Sheet metal can easily cost more than your engine and tranny combined depending on what it needs!