Best monoblock amps for $2000 used

Another vote for the Quicksilvers

Yes, if I were looking for a set of monoblock amps in that price range (2-3K), I would be considering Odyssey SS or Quicksilver tube. The choice would be driven by the speaker system. 

Another vote for a pair of Odyssey monos, FTW!

I say quicksilvers. The Schiit vidars require Balanced connection for monoblock use

Enthusiastically recommend the mono blocks by Electron Kinetics, now EKSC Eagle. The company was originally conceived by John Iverson after the breakup of Electro Research.  
The model 400's were the first mono blocks and many others have followed.  Russell Sherwood acquired the company and has very substantial increased amplifier knowledge that has allowed all Electro Research, Electron Kinetics, and EKSC Eagle products to be upgraded to continue incredible performance from these earlier robust designs.
I currently own a used pair of 11 Prime mono blocks.  Very likely the crème de la crème of them all.
These will be difficult to find as owners are often so pleased that they never let them out of their mitts, even gladly selling their tubed counterparts to own the Eagles!  Look for EKSC Eagle branding as they have been upgraded and will perform exceedingly well.