Hotel Voramar used to charge 100RD per hour per person but I have not been there lately so it could have changed.
They can play at Sea Horse Ranch for 200RD per person per hour. The courts are clay and well maintained there. You can call to check the rates, but I?m pretty sure I am right.
Also, Terramar is another option. I am not sure of the rates though. All of these places mentioned can be used by outsiders. If you are going to Sea Horse just tell the gate you are going to play tennis and they will let you in. Make a right just before the second gate for the courts.