You can try to use NH's long arm statute to sue him in NH, but bear in mind he's a lawyer, and he'll manage to have the NH case dismissed.
Your case is not quite difficult, read the contract clause and all should be clear.
(2) If the contract is clear and the fee is unreasonable, you won't win in court. In that case, you can report him to Massachusette state bar for ethical violation.
http://www.mass.gov/obcbbo/complaint.htm