Getting a good center is going to be tough. Teams are not going to give up cousins, hibbert, Noah, Drummond etc for less than a ransom.
I am not convinced that grabbing a high paid offensive center who doesn't do much on defense is a good idea. That would eliminate Kanter, Pekovic, Vucevic, and some other slow footed bigs.
The celtics might need to build up the other 4 positions and then take a swing at a center when that player is a free agent.
In 2015: Marc Gasol, Chandler (only if he can be stolen cheap, as his game is aging quickly), Hibbert, Jordan, Asik
2016: Noah, Horford (more of a power forward), Nene
And then you never know when a relationship sours and the celtics can swoop in with their stack of picks and young players. maybe a Drummond, Favors, cousins become available in the next few years.
Anyway, i dont think the celtics will have many center options this summer. Maybe Pau Gasol or Gortat could be picked up in free agency. Or Asik could be traded for. More than likely we are going to be small at center again next year.