Just looked and there's one on GunBroker currently. As to what to pay...well, pay whatever he thinks it's worth to him. If it's important enough to have one, money kinda shouldn't be an issue at some point.
There is one at a local pawn shop for $300, I passed because it's pretty rough and has a bent front sight... I offered $250 and they refused. I thought that was fair considering the 60% condition.