My dive buddy and I take the total price of a trip and divide it by the number of dives to come up with a price-per-dive ratio.
It all comes down to airfare though. We luckily fly for free on most of our trips due to playing the Frequent Flyer mile promotions for the airlines.
Our best price-per-dive ratios so far.
1. Cocoview Roatan (free airfare plus 4-5 dives per day make this insane)
2. Blackbeard's (4-5 dives per day, we paid for airfare to Ft Lauderdale and this was still a great value)
3. Cozumel (Christi at BlueXT was able to get us third dives most days we were here, that plus free airfare made it extemely great ratio wise)
4. Little Cayman Beach Resort, Little Cayman (yes, we went in the extreme off-season right before they closed for renovation week, we flew for free and they gave us a sweet deal on our 3 dive/day package, when we got there, they gave us separate rooms for free as well.)
Now, most people wouldn't think of LCBR as a great value and would ignore it when looking for a good value. When it comes to good value diving, going for the low hanging fruit (Roatan) is a good bet, but always make sure to check the places you really want to go since you can get great deals sometimes. We have our local dive shop call places for us and get the prices. This helps too.