Lots of other choices. The Prime rib and Lobster buffet at Cafe Salsa was $46 US for adults and 50% off for kids. Check around for discounts. Ask the bellman.
On its web site is the following note:
The JW Marriott Cancun Resort & Spa the Resort is open with limited services and some visible construction still in process. The Cafe Salsa Restaurant is open for breakfast,lunch and dinner; Beach Walk, our pool side and beach restaurant, is open during the day serving food and beverages, and we also offer 24 hour room-service . Gustino Restaurant and Club 91 will be closed until late summer.
I am not sure whether the buffet is still available or on which nights or at which price.