recommendations on a good used cd player for under $750

I also like a used Rega Apollo. I have one and run a cable from it to another external DAC. So it's just a good transport at this time. I would, if in your shoes, get a cd player based upon two factors beside good sound. One, the best transport system one can find. Two, one that has a DIGITAL EXT OUT so that it may be used as a transport for a better DAC. Sony has made very good ones, even older ones. I like CD players that meet that criteria. Rega and Cambridge Audio do so. Check out the Sony CD-XA20es.

I have the Cambridge 840C, it might be the later version, and the matching amp with balanced interconnects.  I certainly have found it to be nice and it doubles as a hi rez dac, if you can get a hi rez source to it!  Up to 192/24. Either coax or optical. Not USB, etc.  It is good enough that you can hear the diff. with various balanced interconnects to the matching amp.  And I have a 640C which I feel is also a quite good sounding player in my second system with vacuum tube amplification.  But it is unbalanced output only.  Same family of technology and looks.

Addendum, make sure the Cambridge comes with the matching remote control!  Before it I had a Krell CD player.  It was really nice sounding too, but then being older, it developed leaking caps that shorted a power supply and an unobtainium gear broke in the drive.  And the repair est. was at least 900, thus making it impractical to fix based on used value.  So even higher end brands can croak eventually, they are well made but not tanks! 

I second the Rotel 1072. One of the best underpriced players out there.