Hi --
I'm flying into Sanford in August and after much research, opted to rent a car and drop it off the next day at the Car Care Center in Disney. using my Emerald Club w/National, I was able to get a no drop fee. I'll pick the car back up and drop it off at Sanford on the day of my return.
It's a bit of a hassle but it saves me more than $100. I found towncar prices from Sanford to be a bit high (I also have a family of 5, so we need a limo or van, not a towncar). This gives me some flexibility. I wish I could afford to keep the car for the week, but I could not get anything less than $340 or so (including taxes and fees) and I don't think I would use it that much.
Good luck!