Depends on what you deem a "good deal". For my two cents...
Roatan, Honduras has the 2nd largest barrier reef in the world. Direct flights from major U.S. hubs. May is a hot month but a good month because it is after the big Easter week and before schools get out. You can easily find lodging rigth on the biggest beach (west end) for less then $100/night.
We’ll be returning there the last week of May if that’s any kind of endorsement!