Hello - here's my 2 cents worth - every time we've gone to disney we have rented a car for the week. It cost us about $100 US give or take, but afforded us the convenience of coming and going as we pleased. Parking onsite is free, and even at the parks if you are a resort guest.
Works well for us and quite cost effective. We also would make a run to the grocery store to buy water and other stuff.
Check out car rental rates...