I have to agree 100% with MayfieldK. I would suggest around 2.5k, just from seeing his great stop in the very last pic you posted, you can OBVIOUSLY see he is cowy, and wants to get at one. I wouldn't go much over that without him having another great skill. He's bred pretty well, but since he's small and cowy, have you thought about getting him roped off of? If I had to sell as is, I would sell him as a prospect for team penner, a calf horse, or a bulldoggin' horse, as cutting training can benefit any one of those activities, and you'll be more likely to sell him.
Because he's small and has a taste for over-rating a cow, bulldoggin' may be a good game for him. If you can get him dogging, (running past a steer, and OK with a rider sliding off to one side) I think you could probably ask 3 or 3.5k.
Have you considered sending him to another trainer?