A lot of airports have a set fee for a taxi to or from. Sometimes it's set by the airport and sometimes by the cab companies. This makes sense when the airport is separated from the city by any significant distance (or by a body of water, as is the case here in Boston.)

Anywhere from $25 to $50 seems to be the going rate, so I'd say the $70 ladysprite was quoted was possibly unscrupulous. But some cabbies *hate* taking people to the airport, precisely because of the set fee and the fact that at some airports, they are not allowed to pick up another passenger for the drive back to the city unless they have a special (and usually expensive) permit. This was the case in Boston a few years back, and still is as far as I know.