Try mearstransportation.com . Under the taxi section theres a quote option at the bottom of the page. They'll get back to you within 24 hours with a price.
I've been reading a lot on this board about taking a towncar from the airport rather than an airport shuttle. One of the many perks with this option is that they give you a 30 min courtesy stop for groceries. If your party is large enough, this may even be cheaper than the shuttle.
You can check yourride.net for pricing info. This is the route I'll be taking this year.
Hope this helps!
Cara.