When I lived in Orlando, I always used Mears Transportation. They are a large, well-respected company. Disney actually uses Mears to operate their MCO shuttles. In the dozens of times I used them, I never had any problems.

http://www.mearstransportation.com/

I entered a random Winter Garden address and got the following one-way price for a Luxury Sedan: $87 minus 10% for booking online = $78.30. Unfortunately, it looks like Winter Garden is too far out to get a shared-van price.