I'd be fine with paying him $4 million (which is his player option), but if Ainge tries to extend him for another year or two, hopefully it isn't for much more than that. Bass shows flashes of talent, but can completely disappear at times. He's a solid role player, but not a cornerstone guy.
If he picks up the option then that's fine with me, but if another time is willing to give him, say 3 yrs and $24 million, they should move on.