Already suggested, but I'd like to reinforce the Florida keys, specifically Key Largo. Boat rides are short, generally 30 - 45 minutes. The reef diving is exceptional and mostly 30' - 45' depths with more sea life to observe than you can imagine. Viz is typically over 60' and currents very light, if any.
From a cost standpoint, there are lower end motels for under $80 per night and if you want the buddy time with your son on a drive, I suspect you could do the trip for a week under $1,500 for two....and feel like you lived the life of a big spender.
There's also a lot of "non-diving" stuff to do, like visit the John Penecamp State Park and several marine life tourist attractions. You could also drive toward Key West and hang out on some of the more deserted keys one day to kick back and walk the surf with a bag lunch.
Personally, I'd save some of the more exotic places for a while until you both get more experience and your son adds a couple years. I think you'd enjoy and remember more that way.