Most of the midrange boats will be about the same cost as as a similar length stay at a beachfront hotel and meals, less the diving. I'd estimate $250 dollars a day including crew tip for a non-camping (i.e. NOT Blackbeards or bare boat) charter.
For that $ on a diving liveaboard cruise you should get 3 main meals a day, 4 or 5 "snacks" that are almost full meals in themselves, and 4 or more dives a day.
When I charter the whole boat on the Eagle we dive 3 or 4 times the first and last day, depending on the custom agent's schedules, and up to 7 times on all non travel days.
A typical diving schedule day should be.
1. Wake up at or slightly after first light.
2. Fall off the boat/dawn patrol.
3. Early rolls and coffee snack.
4. Fall off the boat.
5. Hot breakfast during first boat movement.
6. Fall off the boat.
7. Brunch & boat movement.
8. Fall off the boat.
9. Lunch & boat movement.
10. Fall off the boat.
11. Nap &/or snack & boat movement
12. Fall off the boat.
13. Clean up a bit and dinner while the crew sets up the evening mooring.
14. Fall off the boat sunset dive at the mooring.
15. Snacks.
16. Fall off the boat for a night dive at the mooring.
Note that generally items 16, 2 and 4 are mutually exclusive as the crew will often not be able to pump your tanks. A couple members of the crew would prefer to sleep sometime and their bunks may be in the same compartment as the compressor. Of course you can always "borrow" a late sleeper's full bottle for the dawn patrol if prearranged. Having a diver come up to go dive and unexpectedly find their empty BC tends to annoy them.
If you work the crew this hard expect to drop a 15 to 20% tip on them at the end of the trip. Plan for it up front and bring it along IN CASH. If the service is not this good the percentage of the tip actually delivered to them goes down too.
This is the diver's trip I EXPECT! Most divers will do 5 dives/day. Some of us are gluttons for punishment though and push the shallower "at mooring" dives. 6 to 8 hours per day underwater is easily doable on this schedule
On a luxury boat like the Nekton expect day rates to at least double, and diving opportunities to drop a bit.
FT