I don't know if this would be an option but we had a family of 7 going out of Galveston a few weeks ago. 2 Kids, 5 adults, lots of luggage plus a wheelchair. We flew into IAH, rented a minivan, and drove to the hotel about 25 minutes from the port. We kept the car all week, found a good parking deal 5 minute walk from the port entrance, and then drove back to IAH after debarking the ship. We had a later flight so it was nice to have the car the entire day to tour around the island, storing our luggage, etc. It was slightly cheaper to rent the car for 8 days and pay for gas and parking than to do shuttles for 7. It was also worth it just to have the freedom to run to Walmart the night before the cruise, pick up dinner at a local restaurant, etc.