You might find a useable mid '70's lemans or grand prix for that kind of money. A decent bumper for a '70 GTO could cost you $2,000.00. I doubt you could find a "salvageable" '70 GTO for $3,000.00 - $4,000.00 unless by salvageable we are talking no driveline, grass growing in the trunk kind of salvageable.
Dave