What do you feel is the best used SACD player?

Just that.
Any of the Esoteric Players. Built to last, hold their value and sound wonderful!
Always the next
For under $500 the Pioneer Elite PD D9 J

I love the minimalist look, build quality and it also sounded great in my systems.

For under $100 if you can find it the Sony SCD-CE595 5-Disc CD/Super Audio CD Player.
Any of the recent ModWright Sony or Oppo players used are a great value. I have also heard a few of the Esoteric players and liked them. Esoteric would be my first choice afte the ModWright players.
Keep looking for a sony 595. Great sound, great value. Spend the money saved on music, live and on media.
the original sony sacd player, i believe it was the scd-1.

it is a great cd player as well.
Don't know your budget, but for about $4,000 you can get a used EMM Labs CDSA designed by Ed Meitner. It has the added advantage of making red-book CDs sound even better than SACD.