I just bought a Dolphin Diagnostic on Ebay. It took about a week to find an auction that didn't go over my pre-set price, but I now have a brand new Dolphin delivered to my door for less that $550. There are several "ebay stores" selling Dolphins, so do a little homework and pay attention to the feedback rating. My experience was great though.

By the way, absolutley love it so far. It's amazing how much crud it will filter out of the water when it looks "clean".