Definitely cheaper than Amtrak, but would you be able to get yourself to an MBTA station, and take the Commuter rail? Or, I suppose you could go all the way to Logan airport on the bus, and then just take the blue line back to the Kinsale. I think the blue line stops at the Government Center station across the street, but if not definitely stops at the Bowdoin station on the next block over from the Kinsale.