Yes, this deal does sound suspicious.
I don't trust eBay. Especially when I see deals like this one.

You were correct again. If it were my money I'd get the S90 or the Motif)ES if possible) and may be the Phantom (although the Phantom would not be my number one choice). But the money is yours, and so is the decision.

If I were you I'd wait 'til I get a chance to actually play a few workstations and compare. You never know, you might like the Triton. Some people do.
You might hate it. I do.

SO really, 'til you've tryed there is no point in trying to decide.

TO answer your other question, a used S90 doesn't go for much less than the new one. They seem to hold their value.
You might find them for less on eBAY but unless you are prepaired to lose some money and time (I'm not saying that you will have to, but it's good to be prepaired.) don't shop there.

-ED-