Here's a great deal from LATAM, fly nonstop from Miami to Punta Cana, Dominican Republic for $252 roundtrip.
This fare is part of their Mega Promo sale that is available until midnight August 7, 2018. Flights are available on this route starting in late September through the end of January, the catch - this fare is only available for travel on Sundays. Even though the travel days are limited it is about $100 less than competing nonstop offers and includes a free checked bag.
Searching on the LATAM site, I was able to find seats departing MIA on Sunday, October 7 and returning from PUJ on Sunday, October 14, 2018. Flights during peak holiday travel are blacked out.
Need a place by the beach? Here's what's available for the listed dates on Hotelwatchdog.