Well, a big part of 'cheap' is where you start from, certainly. Starting from CA, get the biggest delta on flights further west (or 'far east'
) as compared to someone on the east coast.
It stands to reason that even though the flights to FL from CA are cheaper than from CA to Bali or whatever, they are still substantial costs, and enough to kick the total dive trip cost over some desirable threshold for you vs. someone coming 'down coast' from the NE seaboard.
You'd think being in TX I'd get my choice of either - instead I get screwed either way. (Flights from DFW are still on average kind of high, even though American's dominance in the market is on a bit of a downward slide).
I still find the biggest discriminators for me (personally) are the timezone change, and dives/day. Sure, I could probably afford a 10 day trip to Bali with the cheaper costs once there vs. the higher daily cost / lower airfare to stay in the Carribean...I'm willing to bet they'd end up almost equal, at least within 10-20%. But 3-4 timezones I can shrug off as just being tired my first day, and the travel itself usually can be done in the same day each way. A 10-12 hour change equates to me being useless for a day after arrival and ditto on the return, plus the actual transit time. So the trip needs to be LONGER if its further for me to feel like it "equates", since I end up dividing everything by dollars/dive in the end. And liveaboards automatically seem cheaper than doing 2-3 tank dayboats, in general.
Of course it also depends on your ideal diving/nondiving activity distribution for the trip. I definitely am way hard over to one extreme on what I want - but have a wife to make sure I have to compromise. 