Now that you know what it's worth (based on the auction results and advice from members here), you might be able to get a deal on it with some cash in hand. I paid around six grand for mine a couple years ago (in the same part of the state) with fewer original parts. If you're looking for a vintage Donzi to eventually restore and use in the meantime, six grand seems like a great price.
1977 Donzi 16 Ski Sporter, white and orange, 350 Chevy ZZ4, Volvo Penta 270 outdrive turning an Ultra 14x26LH, top speed (June '08): 59 MPH (GPS).