My 2 lire...
Check for a new/used yamaha s90...
If you sequence with your computer, and don't want the sampling functions of the Motif or Motif ES, then you'll be good to go...
If you want a workstation, then you're in the right ballpark...
I won't quibble with anyone over apples & oranges about whose piano sounds are "the best," your ear is probably better than mine, as I've never played a real piano before. The Motifator forum has a fair amount of info from users about piano sounds and such, as well as dedicated forums for Motifs, ESs, and S90s.
You can check here if you choose:
www.motifator.com
There are probably also boards that have only (or primarily) piano & organ sounds, but I dunno what they are, because I've never had a need or any interest. Maybe someone else will offer up some info for you...
Hope this helps.
Diendolo