That's not far from the Boston Public Market, which has a lot of options (Red's Best has a great fish sandwich, Bon Me makes an excellent sandwich, Union Square donuts for dessert, etc). Nice place to browse before deciding what you want.

I once saw someone manage to pull a 4 point U-turn on the BU bridge, somehow stopping the heavy traffic in both directions. They were headed toward the rotary under Memorial Dr, but I guess like most drivers they couldn't be bothered to do things legally or safely.

There is an economy lot at the airport that is cheaper than central parking. You might also look into lots outside Boston but connected by the T -- Revere, for example.

I find it's usually best to avoid parking, either by getting a ride, paying for a Lyft or cab, or taking the T. For multi-day trips its often the cheaper option as well.