I have award reservations at the Frenchman's Reef and for the standard room there was no additional charge. We did elect to "upgrade" to an oceanview room for about $100. per night.
If you look at the rates for St. Thomas, the Morning Star facility is much more expensive than the Frenchman's Reef area. If there was availability at Frenchman's Reef it would not carry a charge. Remember, both are part of the same facility.