Ellydognme, how about a resort course. cost you about a hundred bucks. Granted, you are pretty much limited to inside the reef, but if you've never done it, it will give you a feel for it. Hol Chan is an absolute beautiful hoot the first few times. Lots to see.
Acquire and bring your own fins mask and snorkel. Don't bother buying anything else expensive until you know the difference between good and bad stuff. If you do wish to get certified after that, the States might be a good place to do the classroom (do it in AC and you're burnin precious vacation time but you're not in the water)and then do the cert dives in AC.
On the other hand, if you've snorkeled and feel like you can handle the underwater stuff, skip the resort course, get your classroom out of the way before your first trip and just do the cert dives. The cert dives will take a couple of days, and they are more fun than you might think. Theres a whole different world down there.

P.S. TOAD, get your butt down to AC and join in vacationing the way it should be.

Been there, done that, the washing machine ate the T-shirt