I have to second the recommendation for Avistar - we used them for our January trip (non WDW), and it was absolutely wonderful!!
Previously, we'd had such a BAD experience with the parking lots at Bradley (on airport) that we SWORE NEVER to fly out of Bradley again! But airline prices for our Jan 2002 trip were so much better at Bradley than PVD that we ended up going out of Bradley - we parked at Avistar and LOVED it.
Our bad experience parking at teh airport parking at Bradly was in Jan 2001, and a WDW trip - we arrive at the airport an hour and 15 mins before our mid week late afternoon flight (remember the good old days?). EVERY lot at Bradley was FULL, except the one farthest away from the terminal. So that's where we parked; we saw a shuttle pulling away just as we were parking the car.
We went to the small kiosk to wait for the shuttle (the only ones there at the time). Then we WAITED, and WAITED and WAITED for a shuttle to take us to the terminal - after 25 minutes ONE shuttle finally shows up. It held less than HALF of the people that were waiting - we only managed to get on because I pushed my way through the crowd of people who had NOT been waiting as long as we had.
Who knows when the next shuttle showed up to take the rest of the people to the airport. I had considered walking to the terminal, but there were several problems - we were so far away from the terminal that I actually couldn't figure out which way to go. Plus, either their were no sidewalks or the sidewalks were never cleaned off after teh last snowstorm, so we would have had to walk in the wet and dirty street, carrying our luggage.
We finally made it to the terminal 15 minutes before our flight left - we checked in and RAN to our flight, and they closed the doors after us. When we returned, it had snowed, and we also had a little difficulty getting into the car to get the scrapers for the windsheild (car and surrounding area covered with snow). For all of this annoyance we paid $50/week; we were gone for 10 days, and price was approx. $85.
With our Jan 2002 trip, we drove into the Avistar parking lot - filled out a form that took about 1 minute (name, address, phone, airline, return flight, car registration/license plate etc). You leave your car with the keys in it right where you pull in. There was a shuttle waiting for us, already warm. The driver took our bags out of our trunk, and put them onto the shuttle. One other couple had pulled up at the same time as we did, so the four of us got into the shuttle, and we left! Took about 2 minutes to get to teh termina, maybe 4-5 mins total from the time we pulled into the lot.
On our return, we used the courtesy phone in the terminal for Avistar, gave them our ticket number, and waited approx. 5 minutes for the shuttle to pick us up. The car was waiting for us, started, with the heater running, and was warm by teh time we got to it. I went into the building to pay ($35/week plus a couple days), ended up being about $55 for the 10 day trip.
We were driving home before the poeple who parked at the airport parking had even gotten to their cars!
Use Avistar - they're GREAT!