It seems that with Grand Sirenis you buy a number of weeks then you have no MF. I assume that they hit you hard after with the AI fees.
Here are the AI fees as posted in Diamond Resorts resort directory.
Grand Sirenis Riviera Maya Resort
Akumal, Mexico,
2018 Standard All-Inclusive Rates
Studio - Adults (ages 13+)
May. 1 - Dec. 22: $160
Dec. 23 - Jan 1, 2019: $260
2019 Standard All-Inclusive Rates
Studio - Adults (ages 13+)
Jan 6 - Apr 30: $210
May. 1 - Dec. 22: $170
Dec. 23 - Jan 4: $300
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Grand Sirenis Punta Cana Casino and Aquagames
Punta Cana, Dominican Republic
2018 Standard All-Inclusive Rates
Studio - Adults (ages 13+)
May. 1 - Dec. 22: $160
Dec. 23 - Jan 1, 2019: $260
2019 Standard All-Inclusive Rates
Studio - Adults (ages 13+)
Jan 6 - Apr 30: $210
May. 1 - Dec. 22: $170
Dec. 23 - Jan 4: $300