That's a cool bike but not so cool at $400. I've never seen a Grand Prix from that era bring over $250. I've seen a couple of these listed on CL here in Houston that started out at $350ish and they sat, then the price dropped and dropped until it hit the low $200s and then poof... No more Grand Prix on CL!

On the other hand, look into what the overhaul consists of. That bike needs new cable housings and bar tape (if only for proper aesthetics), probably tires and maybe a chain. This can be worth $100+ since it's real cost you'll likely incur yourself.

i still don't see it bringing $400 but maybe you can negotiate lower and have some new stuff on it.