We have used Tiffany Towncar when arriving at Sanford. But that was back long before we realized how easy the drive is to WDW. The cost is about $200, not including a tip..so a fairly sizable chunk of change.
A rental car could be a lot less if you are using it just to get there and back, and not keeping the car for your entire stay. But I have also found a rental that cost less than the car service, for my entire stay.
The drive is easy and pretty straightforward. The car rental counters are just outside of the baggage claim area, with most car lots right across the street....not a main street.
Check out costs both ways and see how it comes out.