I just came off a one week Caribbean cruise on Regent Seven Seas Mariner. Cruise fare (all in)) was $3099 per person minus my onboard booking discount. I also chose to do my own air so I saved another $400 per person. TA also gave me 5% back. Between Amex, Regent, and TA benefits we had $1100 shipboard credit. Therefore, my net cost for cruise was around $5500. Almost all excursions were included but I splurged for a flight to see Tikal in Guatemala. Remainder of shipboard credit was spent in spa or shop.
I spent some time in casino; craps table was good to me. Casino is small but they have craps, roulette, black jack, and I think Caribbean stud.
Regent has a series of Caribbean cruises in winter. Alas, starting in fall 2011, most of them are 10 day instead of 7 day cruises.
My total bill getting off the ship was $0.