If you can find someone with a local library card, stop by any library in the BPL or Minuteman system (Somerville is Minuteman). Go to the reference or children's section (depends on the library) to get super discount coupons for museums all over the area. The coupons can also be use for non-residents/library card holders.

BTW, this also goes for locals - the savings are truly spectacular. I had four family members vacy in Boston; our trip to the Museum of Art would have run $100, but the coupons knocked it down to $20 total.