Theres one in Lynn. On the corner of Parkland and Walnut. Not sure if its directly on a bus line,( I avoid the T like the plague ) , but Walnut is a fairly main road and Boston street is just a couple of blocks south of there. Really small place tho.
Danvers Fish and Game on 114 in Middleton near North Shore Voc., again, not sure about being on the T, but should be easy to check.
Eastern Rifle and Revolver Club is the one in Lynn on Walnut St. Currently they are full and not accepting new members (as of two weeks ago). They are dirt cheap if you want to wait until January when they expect to have some turnover. $190 plus an NRA membership if you don't already have one then either $90 or $100 for renewals (I forget which). On the other hand, it's a pretty limited facility - just a small pistol range in the basement. The guys there are very nice and friendly, so if that's what you're looking for, it might be worth waiting two months.
I joined Andover this month - getting sworn in on Thursday. Looks pretty good and has lots of good reviews from members. Not much more expensive than Lynn, but probably much harder to get to on public transit.