Well it obviously is not a fastback nor a GT. What size engine does it have? 200 straight 6? 289 V8?
The car looks to be on good condition, however coupes are not nearly as valuable as a fastback. The engine will dictate what you can sell it for really, because if it's a 289, you should get $7,000. If it is only a 200, then its probably more like $5,000 ish. A car is only worth what someone is willing to pay, so start by asking $7,000 .. even if we think its only worth $5,000.
Good luck, nice car by the way.