Best monoblock amps for $2000 used

I'm curious as to why you want to go for monoblock amps on a limited budget.
Generally, you get more bang for your buck with fewer chassis'.
I would think that $2000 would get you a better stereo amp than monoblock amps. 
$2500 would probably get you a better integrated amp.

The more chassis' you want, the more $$$ you will need to spend.

Go fishing for MFA monoblocks.

Wait until they appear. Be stubborn.

Just checked. Gone the way of the dodo bird. The odd used set used to appear. None around, all in people's systems and not coming out.

I would be looking for tube amps. My speakers are Silverline audio
Sonatina Mk IV's. I listen to mostly jazz, and some rock from the 60's
and 70's. Room size?It's an open floor plan, with the listening area
probably 14' by 18'.

I seriously doubt you can find ‘quality’ and newer tube monoblocks in your price range. 

While you considering your options, I would recommend looking into ATI’s Class D amps, I own a pair of 544 series amps and they are quite amazing. 

http://ati-amp.com/AT52XNC.php

Prepare to pay more for monoblocks as jmcgrogan2 pointed out.