Jenny, MV and Newport are great, but tend to be pretty pricey in the summer. The Cape mainland can be a little more reasonable, but you'd still have a hard time finding a place for less than $250 per night. If you're going for the week, you might be able to find a last-minute deal on a condo or house rental. These sites should be helpful. Let me know if you have any specific questions- I also went to college in Newport but it's been a while.
Cape Cod Vacation Rentals and Florida Vacation Rentals - MA & FL Summer Beach Homes
Martha's Vineyard Hotels, Accommodations, Real Estate, Travel, Restaurants, Inns, B&B, Bed and Breakfast, Rentals, Properties, Vacation Rentals - Home - Martha's Vineyard Online - The Official Site of Martha's Vineyard