Well, I know two dealerships are selling left over '05 for $20,000 and $19,500. MSRP is $21,500. Pro Italia does have a left over 2005 two seater and a 2005 single seater. Beaudry Motorsports also has some leftover 2005. Here's link to their sites:
http://www.proitalia.com/mvagusta.html
http://www.beaudrymotorsports.com/cgi/bmsinstock.pl
Renaissance Motorcycles in Tucson, AZ has a brand new red/silver 2003 750cc F4S and I'm sure they'll sell it at a good price. They also have a new 2006 MV two seater. The 2005's MSPR is $21,700.
http://www.ducati-az.com/
I've seen some used 1000 on Cycletrader and they were going for $18 to $19K. For that price, I'd rather go new on a left over '05. Used 750s are going for $10 to $13K but I really dont' think you'll be happy with the lack of torque on the 750 coming from a RC51.