I would look into PreFlight parking....it's a bit offsite. But, they have a shuttle that picks you up, right at your car, and runs continually. If you go to their website, you can print off a coupon that will save you some. I find this is a great solution...especially during the non-winter months!!!
Even if we use a shared van from central Mass to Logan, it costs close to $150. And a car service is even more!!!