Moving and waiting 12 months to matriculate will qualify the OP for resident tuition in most (maybe all) states. Therefore the grandparents option is viable, though as M2CK said, public colleges in Massachusetts aren’t particularly cheap. There are exceptions, like the Massachusetts College of Liberal Arts (MCLA), but that school may not have the programs that the OP seeks. And the grandparents may live nowhere near MCLA. Another decent Massachusetts school is Worcester State College, which has a great cross-registration agreement with other schools in town, including Worcester Polytechnic Institute, which does have an Economics Department.
All that said, I still believe that Norfolk State University and Old Dominion University are better (cheaper) options.