I guess it just depends on how much money you're willing to spend up front versus 'along the way'. I see '70 to '73 Firebird 'projects' for sale quite often on Craigslist and Ebay that run anywhere from $1000 to $5000. I've seen a few actual T/As that were in bad shape and not running go for about $6000. When you add up the price of all the parts and rear body work necessary, and 'time', well, you can see the value there.
Here are a few out there for sale right now:
http://fresno.craigslist.org/pts/1505994386.html
http://milwaukee.craigslist.org/cto/1519696263.html
http://www.cardomain.com/ride/2247778
http://maine.craigslist.org/cto/1508602425.html
http://dallas.craigslist.org/ftw/pts/1513237182.html
http://redding.craigslist.org/cto/1507337691.html
http://medford.craigslist.org/cto/1507256458.html
-Chris