Several years ago we rented a beach house in Garden City Beach for 3 nights for a family reunion. We chose one block off the ocean and rented through Dunes Realty. It had a nice pool in the back along with patio and grill where we cooked out. Dunes couldn't have been any better to work with. They specialize in Surfside and Garden City.
http://www.dunes.com/Their website says:
Nightly- All nightly rentals are subject to availability and a minimum stay required (2 nights in condos, 3 nights in houses.) Call us for restrictions and availability. Discounts may be available for 3+ nights in the same property. 888-889-0312
http://www.dunes.com/rentalinfo.htmYou should also check VRBO and HomeAway for owners who may be more inclined to rent for a few days rather than a week.