The FDIC would be forced to levy a special assessment to all Banks, based upon asset and deposit size. It was done previously during the financial crisis.
?? NewBie with no knowledge of 'Grand Theft WaMU'??? Why would FDIC 'pay' anything? It would be JPMC that has to pay up to 'consummate' the Acquisition, FDIC would only be the 'conduit' (Of course, assuming that FDIC/JPMC will proceed on to doing the 'right thing' here with this taking of WaMu). So all your musings about 'special levies' of FDIC are irrelevant/not applicable in our case.
I believe, that it has been stated that the FDIC has a 'backstop' from the US Treasury of 500B dollars. That seems quite a large number to have been used, early in this fiasco, if it's need wasn't already foreseen.