Looking for a solid state preamp for Krell fpb 250m monoblocks

As a fan of tube preamps, there is only one SS preamp that I could recommend, a Klyne 7 series preamp. Very natural sounding, IMHO.
They are very hard to find on the used market, but if you are patient, you should be able to find one in your price range.

All I've used are tube preamps with all my Krell amps over the years, starting with KSA100s and never a problem.    The old Krells are a bit bright and hard so always prefer some tubes in the chain.

In your budget, checkout an used ModWright LS 36.5 DM.

I recommend a tube preamp as well, I think if your not careful you could be adding a lot of coolness and edginess to your system. A tube based pre would add much needed warmth and the Modwright is a good choice but I would also check out a Manley Jumbo Shrimp, or a Doge 8 clarity, or Dehavilland Ultraverve 3 or a Audio Research or Conrad Johnson. All well within your budget.

Matt M