Greetings,
Assuming your starting point is the OIA, and unless you really like shuttles, I highly suggest the towncar services. I tried one last time and I will never go back to the shuttles. I used http://www.tiffanytowncar.com/ last time and it is between $75 and $90 round trip depending on where you are staying. There is even a $5 coupon on their web site. While we are just a family of three, it would have cost us the same for the shuttle.
Regards,
James