I've got a PX-320 (and 310 before that one) and try to turn them over every 1-1.5 years to keep up / minimize loss. I saw a thread on PW a few nights ago discussing music123.com having them on for $559 back in Sept / Oct 09.
As the 320 is pretty good, I wasn't feeling extremely pressed to upgrade, so I REALLY needed a good deal to get me motivated. I was close to a Guitar Center last night (where I've bought my last 2 privias) and so figured I'd give it a shot.
They wouldn't negotiate at all on their own but I 'explained' that there were instances of music123 selling at $559. He called them pretending to be a customer & sure enough, music123 agreed to honor. So they beat the price. Think it was actually $545 on my receipt.
I didn't feel too bad as I'm sure the vast majority sell at the $699 gouge price, plus stand, plus bench, plus warranty etc... If that doesn't work out for you there is also a music store selling B-stock for around 550 shipped on Ebay.
Anyway, I hope this helps someone as the other thread sure helped me... I did pay $30 in tax but wrote it off to instant gradification and helping out Caesar