I agree with the PP that you'll have better luck if you can expand to Houston for your search. I know of one national company that rents there and if you talk to them they may even be willing to deliver to Galveston for a fee (actually just found something for their Houston area rentals that says they includes the entire metro area including Galveston, so there may not be an extra fee). Most local companies may do the same if you ask, even if they don't say they will. You can always call around and find out who has the best price once you find places that will rent.