Hi, Jennifer! When staying off property, we always rent a car. It just makes things much easier for getting around. This will also give you the flexibility to run to the grocery store for snacks and food for your room. (Publix is my store of choice when I'm down in that area!) You can also be on your own schedule and not have to wait for a bus.
There are many car rental companies to choose from. I like to use Dollar because their cars are on-site and I don't have to take a shuttle to get my car. I also find they have good rates but you can look around for the best deal. You might also want to go to
www.mousesavers.com and look up any discount codes they might have for the rental car companies. Try with and without the codes, I sometimes find it is cheaper to NOT put in a discount code!
One additional cost will be parking at the theme parks. The cost is $14 (subject to change) but this does cover your entire day even if you park hop.
By the time you pay for transportation to and from the airport and shuttles to the park, it will probably be best to just rent a car. I think you will also enjoy having your own wheels in case you want to go to Downtown Disney, a restaurant or one of the great shopping areas! Hope this all works out for you!