best thing you can do is go to eBay, and start scoping out what the high bids are, NOT THE BUY IT NOW, but the what people are actually bidding. See stuff you like and then put it on your watch list to keep track of it.
Theres WAY too many variables, but assuming nothing special youre gonna spend 6-10K on a motorless and trannyless 70 in ok shape. Even a total turd will bring 4K.
How much of a project are you looking for other than the Motor ? Paint, interior... ?