I think Carnival tends to be cheapest. Remember "booze not included" so you will run a tab and get a bill at the end. Make sure you are prepared for this. If you are going to spend the week saying: "Hmmm, I'd like another drink but don't want to run up the bill", then it's not really a vacation. I tend to prefer an AI resort for that reason.
Cruises are not expensive, its the flight to FLA that kills ya sometimes. Check cost out of Buffalo. My sister saved almost $1000 two years ago for 4 people. She's going again next week, the savings was only a couple hundred so she's just flying outa T.O. Another viable alternative, if you have the time, drive to FLA. It's a easy drive (21-24hrs)
Life is like a sh!t sandwich...the more bread you've got, the less sh!t you have to eat.