For an idea of prices, you can also check HAL's shore excursion list for HMC. Good friends of mine rented the Palm Package (a very large cabana) a couple of months ago and said it was wonderful. While this one is intended for a large group, I've heard the cabanas for 4 are nice, too. For an extra special touch, you can add a butler package. I don't believe, though, that any are poolside -- I don't even know if there's a pool on HMC.
Here's information on Half Moon Cay pricing
from HAL's Web site. (Carnival's may differ but probably not by much.) I believe the pricing is per cabana, not per person as it states. I also found a photo montage
that someone put together that not only shows what the cabanas look like, but their relative distance from the tender dock.