IF KG wants to keep playing with the C's, he might be the most valuable free agent to sign. Suddenly the cap space will be small enough, that it makes more sense to bring back just about everyone on short deals and then target a MLE big.
MLE: Kaman (although he might be worth more), Camby, Hawes, or bring back Wilcox and a raw prospect like Orton.
If KG retires/leaves, then the full rebuild will begin. This free agent class doesn't seem to have anyone worthy of a max building block deal. (I'm not convinced Deron Williams is going to be that big an upgrade over Rondo).
I would then see if you can steal Asik, McGee, Hibbert, Mayo, Lopez, Fields, Batum, etc for something in the 6-9 per year range (certain guys listed are more valued than others for sure, bu ultimately probably matched by their current teams.)