The resort course is a waste of money in my opinion unless you really never plan on diving much. Give this a shot. Call your local dive shops and see if they do a try scuba or discover scuba. If they are a good shop they will. It is a chance to get in a pool with supervision, try the equipment and play around and see if you even like it in an controlled environment. Usually runs around $10-50 bucks.
If you like it, most shops will apply the fee to a class. My suggestion is do your pool and coursework at home then get a referral letter to do your open water/ checkout dives (kind of like your final exam to show your skills are up to snuff your learned in class) in Belize. Your dive shop can give you more info on this too or check out www.ssiusa.com
the two prevalent certification agencies for more info.
The cost for a resort course runs around $150 but you are not certified and have to pay that much each time you do a resort course dive and have to always dive with an instructor. Full on certification with pool and classroom training runs about $199 -$250 then the open water dives are extra (cost dependent on where you do them about $225 in Belize). You also should budget for a basic set of equipment too - mask, fins snorkel and booties for probably around $300.
Probably the best thing to do in my opinion is talk to your local shop, tell them your level of curiosity/interest and let them guide you into making an informed decision. Don't be afraid to ask questions or tell them if you are working within a particular budget too.
If you like the water, you'll love scuba and be hooked. Good luck on your new adventure