Renting a car for the week usually cost more than the car service price from that airport. I have seen prices from $200.00 to $350.00 a week for moderate to SUV vehicles. Not sure what the cheapest would be but it is not much less than $180.00. I have also been told by passengers that the rental cost to using the vehicle at WDW is not worth the difference in the rates they could have got for the car.
A car service will charge somewhere between $180.00 and $230.00 round trip from Sanford. Taxi meters run a little bit more. It is a direct drive to Disney about 50 minutes, with a grocery stop, if you like. Transportation is free at Disney so you don't need to use a car there. You don't really blow all your airfare savings out the window using a car service. The convenience and time a car service provides over renting and trying to find your way around and down to WDW might be worth it to some people.