Personally, I will NEVER AGAIN use Mears. We ran into a horrible delay with them. It was very difficult to even get picked up at the airport. You hurry over to the pick-up area (all your luggage in tow) and arrive just in time to see their tail lights. Then you have to wait 30 minutes or more for the next - and it was full. By the time the 3rd van stopped, even though it too was full, we squeezed our way on board. The ride was very cramped and humid. Then it seemed like everyone else on board got dropped off before us...and the driver got lost 2 times between MCO & WDW (other stops were NOT at WDW). This was the LAST time we used MEARS.
We had used them twice before with SOME delay and a bumpy, uncomfortable ride, but this last time was the worst. To us it is just not worth the money. We rented a compact car for one day and drove ourselves to WDW, stopping along the way for groceries/snacks. We used
Alamo and turned the car in at the Car Care Center at WDW. Then we were going to rent one again for our return trip, but some people we met at our hotel offered to share theirs as their plane was leaving about the same time. We split the cost of the rental.
I think the idea of a towncar is the way to go. Several of them will make courtesy stops at a grocery for you if you let them know ahead of time. They will be waiting for you at the airport and their cars are nice and comfortable. They take you directly to your hotel!
Just my 2 cents, but as I age, creature comforts take a little higher priority than $$$. And, considering how much the rooms and parks cost, you really want to get to WDW and begin enjoying your trip ASAP, right?
Have a great trip.
It's nice to be able to have a little freedom if you want it. This time I'm using Dollar for $78/5 days. I've gotten National for $144/8 days too. Lots of playing around with the codes and whatnot. 
