Was in similar situation a few years back, wanted a cheap, quick tropical getaway. Went to Punta Cana, DR on charter out of St. Louis.
Was really cheap (under $500 per) but is Punta Cana is really only good for getting drunk at the beach/pool. No nightlife, food is pretty crappy, etc.
Super easy trip, drive on I-70 to St. Louis was the worst part.
HTH