I purchased a Marquis/Everyday 2005 5 series tub new in Feb of 2006. It cost approx $6,000 (tax, delivery, everything). I've been very happy with it.
I do not know the used hot tub market, but knowing what I know now, I'd buy that 415 for $2000.
I think the tub is well made, reliable, and that seems like a good price if it's in good condition.
For what it's worth....
David