I guess it depends on where you're staying at US. If you're staying at a US resort, you'll be paying to park, daily, if you have a car. Then, there's gas and the cost of the rental. Uber, or Lyft, from MCO to US, shouldn't be too expensive. It's only about 20 mins away. I know it's about $40 each way from Clermont to MCO, and that's a 45 min ride! Then, from US to WDW is about $14. Then use DME back to MCO from WDW. Unless you need to have the car for some other stops, using Uber or Lyft may be the most economical way to go. And you don't have to worry about driving in an unfamiliar place.