I looked into this and could not find any hotels that offered shuttles from the airport to Galveston. As for cost, Hobby airport is a much cheaper taxi/town car ride ($80/$90 one way vs $140/150 one way from IAH). The cheapest options I found if you have 3 or less people and don't want to rent a car is to (1) use the Disney transfers ($30 pp each way) and stay at the Disney assigned hotel (the issue here is the hotel is fairly pricey on the night we wanted $200 plus) or 2) take a taxi/town car one way to a cheaper Galveston Hotel and then Disney Transfer back.