Without passports I would recommend Hawaii (Big Island) or FL Keys for warm water dives. The Keys are probably cheaper - you can fly into Miami, rent a car and drive 1 hour to Key Largo. 3 to 4 star motel room rates can be as low as $80/night in summer. In KL, my favorite dive ops are Ocean Divers and Silent World, both are friendly and safety-conscious (OD has 2 dive boats offering a choice of dive sites; SW is lower priced and they sell gear at competitive prices). If you'd rather head to Hawaii, in Kona (west side of Big Island), my favorite dive op is Jack's Diving Locker. Great dusk dives to see feeding manta rays and hunting moray eels. For all these dive ops, there are significant discounts if you do multiple dives with them.
PM me if you need more info. Good luck to getting your OW c-card!