This link is helpful: http://www.bc.edu/admission/undergrad/visits/campusvisit/hotels.html
We personally find these three hotels to be especially reasonable and convenient when travelling by car:
Crowne Plaza in Newton
Hotel Indigo in Newton
Westin Waltham in Waltham
Of the three, Westin in Waltham is the least expensive. Although it is in Waltham, it is just a quick drive to BC.
And don’t forget to ask for the BC discount!