Some things you may find useful:
Probably the cheapest flights are to Cancun if you want to start in Mexico. From there you can do the bag/drag to Cozumel - it's generally several hundred dollars cheaper than flying there direct. Bus from near the airport then the ferry over. Described in detail in a post in our Cozumel forum.
The ferry leaves from the Playa Del Carmen area - also good diving. Then head south via bus - Tulum has both diving and a Mayan ruin right on the water - probably about the only place that exists.
Make your way down to Chetumal and the
Belize Water Taxi will pick you up for Ambergris Caye, Caye Caulker or Belize City. If you want to detour to south Belize (Placencia area) Tropic Air flies down there for about $90 one way. Dive with
Splash Dive and they;'ll pick you up at the airport, take you to your lodging and pick you up for diving.
From there one option might be to fly onto Honduras via
Tropic Air - they have weekly flights to Roatan where you can also catch the ferry to Utila. In Roatan's West End there's a couple of hostels and a whole lot of under $50 small resorts - that buys you a small apt. with kitchen at some. The hostel in town -
Chilies - also owns Native Sons Diving. We used
Coconut Tree Divers in the heart of town, their boats are across the street and they have a pretty good Roatan/West End info page on their website.
There's at least a dozen other shops in town and boat dives are currently 10/$350. Food is also real cheap, there's small restaurants, the food trucks sell fish/produce on the street mornings and there's a couple small stores in the area. We didn't even rent a car all week - the whole West End is walk able. I believe the fare from the airport is about $25 if you fly in.
You can also take the
Galaxy Ferry from La Ceiba on the mainland to Roatan - it docks in Dixon Cove.
The
Dream Ferry also runs between Roatan and Utila on weekends. It ports in the West End afaik and the public dock on Utila. Most of Utila lives in town, it's a backpacking destination so rooms start at $10/nt. and the diving is also around 10/$350 in town from what I was told as there's also a lot of competition there.I believe during the week the Dream runs between La Ceiba and Utila - probably replacing the Utila Princess?
I know someone who goes to Costa Rica to dive regularly. I'll leave that up to others since I've not been there.
sounds like fun...