We have Happy Limo taking us from Portofinio to Epcot and back. My sister made the reservation so I'm not sure of the cost. www.happylimo.com - sometimes you can use a coupon code with them (OTP1277) to get a discount on transfers (not sure if this is for airport transfers only or not).
It depends on how many people are in your party. Mears runs shuttles for about $14 per person round trip. If you have a large group, it's cheaper to get a taxi or town car.