Best Class A Amp under $2,000 used?

Class A does often sound very good - I used Classe DR3 VHC which with 45 watts will drive low efficiency speakers like Apogee Scintillas, and Belles A.

I don't think you will find, nor need anything like the Class A power you are asking for to drive just about any speaker out there.  You'd be amazed what amps that are well under 100 watts in true class A can do - but you may want to consider that they are running all the time, putting out anything not used in amplifying signal as heat. In one system I run a pair of DR3 VHCs and in summer it gets pretty darned hot in there.

Others made pure Class A amps of modest output - Electrocompaniet, Bedini, and they would drive the heck out of very difficult loads. 

For $2k you should be able to pick up some A/B amps with sturdy power supplies that will give very good sound - if you were closer, I'd offer you a Rowland I have for sale!

if you can find them NRG A400 will give you what you want not sure if you could get them under 2k, I don't know anything that can touch them.

Might I suggest a different direction? 1) a pair of Crown PS-400s. ($700-$800 used) Heavily biased into class A, plenty of power,excellent specs,bullet-proof build quality, and sound pretty darn good! A Crown Macro or Studio Reference these got an A rating for sound quality from TAS,Stereophile and other audio mags, unreal power 760wpc-8ohms,1,100wpc-4ohms !
($1100-$1500 used) Best of all but hard to find for your price. Any of Jeff Rowland,s bigger amps.  They all sound great!

...he's not listening.

Perreaux PMF 1850. 170 watts of Mosfet power..  can't be beat for sound quality and will cost less than $1000.00.