Sullivan Square parking for the Orange Line has always been my go-to. It's right off 93. It's $9 to park on a weekday, $6 on a weekend. A one day pass to ride the T is $11.

From Manchester you can zing straight down there, park relatively cheap, and take the T in to the city. If I recall correctly, the Sullivan Square stop is only a few away from the changeover opportunities to the Green and Blue Lines. You can also get to the Red Line a few stops further down.

You can get anywhere between those 4 lines. You've got about 50 miles of gas to pay for, and then $20 covers everything else.