Eagle reimburses me $80 a month for
not using Preflight. I'm on the cape & use the P&B bus - you should have an equivalent service, Concord Trailways? or Dartmouth? Its $90 for 10 one way passes, parking free at the Sagamore bridge. The Logan Express bus passes are $75.00 for 44 trips, but monthly parking is another $66 or so, I'm not sure of the geography on the north shore, but Woburn, or Peabody are the northern terminals.
Check with the info desks on the baggage service level to find out which bus lines run to your vicinity. Then go to the parking violations office in Terminal C - they only sell the discounted bus passes there - not on board or at the suburban stations. You'll need your company badge, no Logan ID required, and pay only by Visa/MC.
Also click here
http://www.massport.com/logan/getti_typeo.html
for Massport's links to transport options.