Be straight with him. Tell him he’s getting low balled, but if he really wants to let it go that cheap, you’ll give him $310k. Or, if you really think it’s a good deal or really care about the guy, make him an offer that won’t expire for two weeks or so. He can try to get the great big offer, when he doesn’t he’ll appreciate that you (a) gave him that chance and (b) paid a little more than the bottom feeder.
I think friends are worth alot more than money, and mixing the two always carries risk.