Correct price is really subjective, but i agree, I would never pay that much for unlineaged gliders and certainly not if they weren't well socialized. To me, it sounds more like he has a pair that he's breeding to make some extra cash rather than genuinely "rehoming." To put it in perspective, I sell my lineages 50% leu her grays for about $250 with breeding rights, much less for pet homes. I currently have a pair I'm selling for $400 WITH a neuter for the male, and these are joeys that have been handled from day one.
If it all sounds fishy to you, or the guy just gives you a bad feeling, don't let yourself feel pressured. I'm certain the collection of heads on this board can help direct you towards a better match if need be.