Princess Cruises is offering some very tempting rates on a 26-day repositioning cruise which includes a nice array of Greek port stops. Of course, they don't label it as a respositioning cruise, calling it the "Mediterranean and Greek Isle Grand Aventure" instead, but this across-the-Atlantic spring cruise certainly qualifies, and has the low pricing to match. It disembarks from Ft. Lauderdale, Florida, on May 1st, 2010.
What I like about this one is that it offers a full week in the Greek Islands at the end of the cruise.
While its final port is Venice, you can choose to disembark in Athens by special arrangement, which may even shave a bit off the already-low price. Interior cabins start at US $2535, excluding taxes of about $150 US. However, on a cruise of this length, I'd opt for a window view or mini-suite which runs about $4300-5500 per person, double occupancy. But, remember, repositioning cruises are in a sense trips the ship itself wants and needs to take. These prices may tumble even more.
The down side? If you're not a cruiser at heart, the 8-day trans-atlantic passage may be a bit hard to take, even on the Crown Princess, a ship with a full range of luxurious amenities.