Best Class A Amp under $2,000 used?

Listen to a Parasound Halo. They're very good for the price. 
By coincidence, I have one for sale. 

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.