I recently had this same delimma. We had plans to stay at Pop our first night in Orlando (flight gets in 1015pm) and after decided to do the next day (our first day) at Universal to do Harry Potter. After lots and lots of research, I came up with this: cheapest WOULD be the Lynx bus, but a complete hassle. Especially with a 7yo. Most expensive would be cab (around $90+), followed by a towncar rental ($81), then the Mears Shuttle ($60ish for 3 of us). I got a code, however, from Mousesavers.com for National Car Rental, and got a fullsize car (think Impala) to pick up upon arrival at the airport, return at the Disney Dolphin the next evening, for $50, + unlimited miles. It was by far our best option! Plus being able to rent it at the airport, and return it on Disney property where we won't need further transportation, is awesome! (We have also since cancelled our Pop reservation for that night and got a room at the Crowne Plaza Universal off of Hotwire for $70 so we'll be closer on Sat morning).