The cost may be pretty low but not because the FDIC will somehow get the nominal price for those bonds. They are not worth more than what they are worth. (On the other hand, they are worth more now than they were on Thursday.)

Worst case scenario they’ll probably end up sold to the Fed and held till maturity like all the MBS the Fed bought during the pandemic.

If I'm not mistaken those were bought at "reasonable prices" - not at par.

The FDIC will probably just hold them to maturity and go running to congress if they need more liquidity at any time.

There would have been a massive drop in asset prices for the companies impacted by losing their deposits.