I don't think the Kings would consider that a godfather offer. I expect that other teams, the Cavs for instance, could and would make much better offers.
Right now the Celtics have one legitimate all-star (Rondo), one borderline all-star (Green), and a bunch of role players. I consider both KG and PP role players because they shouldn't be playing full-time starter minutes at this point of their careers. I consider both Bradley and Sully super role players because they offer a lot but are not really complete players (Bradley, due to his offense, Sully, due to his lack of size (and injured back)).
I think the Celtics only shot at Cousins is to pool all their assets outside of Rondo and Green and hope it's enough. I, for one, think the potential of a Rondo/Green/Cousins core is worth it. You fill out the roster from there (and have a 5 year window or so with that core).
To pool their assets, the Celtics could try to expand the trade with SAC to include LAC. It would look like this:
BOS receives: Cousins, Salmons (salary dump), Hayes (salary dump), Butler
SAC receives: Bledsoe, Bradley, Sullinger, Pierce (buy-out), and BOS 2013 1st round pick (16)
LAC receives: Garnett
It all depends on whether you think Cousins can be 1B to Rondo's 1A on a championship contender (I think he can). But I really don't think you're getting him for less (and it still might not be enough). In the NBA, four quarters generally won't net you a dollar.