The strength of the dollar will probably make the most difference to foreign visitors, but New England can be fairly expensive, especially in Boston, Cape Cod, and resort areas.

At the budget end (staying in hostels, rarely eating out, walking and visiting mostly free sights), you might be able to get away with about $100-150/person/day.

A more average budget for most visitors (staying at standard hotels or B&Bs, eating out once a day, going to the full range of sights and taking public transport), would be $175-250/person/day.

Double that and $450+/person/day buys a pretty high-end experience, with luxe hotels, meals at the full range of restaurants, and taking taxis around town whenever you feel like it.

Note that traveling solo will probably raise any of these per-person-costs by at least a third for all except budget travellers.