Those seats look pretty nice. Recently Upholstered? I have sold benches out of chevelles/skylarks etc same bench for 150-200 bucks and they needed new foam new covers etc. Really just solid springs and tracks.
That being said if your seats dont have any tears or anything I would think 300 would be a fair asking price BUT that I also know that alot of upholstery shops charge 300 or less to do a seat all the way through. You would get the most out of someone who needs a seat as in doesnt have one at all.
Imo i dont think you could trade straight across for factory buckets. :no: