Ainge couldn't get much for Bass in the past because Bass had multiple years left on his deal which made him hard to trade. Not many teams were interested in giving up a good trade package + paying Bass a high salary at $6-7 million a year + being stuck with multiple years left on his deal.
Now that Bass is in the final year of his deal, he is much easier to move. Ainge has a fair shot (not a sure thing, but fair chance at it) at getting a 1st round pick (or a decent prospect instead of a pick) and cap filler from some playoff team that wants to boost their bench heading into the playoffs this year. If Ainge was willing to take back contracts with another year on them, I fully believe Ainge could get a 1st round pick for a productive veteran like Bass -- but Ainge would have to value the pick over the cap space next summer. Depends on where his priorities are.
Once Bass' contract ends .... Bass is a skilled PF who has a strong jump-shot, plays plus defense and has considerable playoff experience. Bass is one of the best backup PFs in the league. He will be a highly sought after player. Under the old CBA, I'd have expected Bass to generate multiple offers of around $5 million per annum ... so maybe $6-7 million under new CBA. He will have a large number of suitors -- mostly playoff teams, at least 4-5 teams if not as many as 7-8 teams -- who will want him. His skill-set and experience is highly desirable in a bench player. Who knows, maybe Bass gets lucky and some team even offers him a starting gig and $8-9 million a year. But large majority will view him as a backup PF and price him lower than that.