My son wanted small school, so marching band was impossible for him. Playing in a pep band, though.
Medium sized, walkable downtown, PA proximity, not a full pay private is doable, if by medium sized you are open to schools in the 10k-20k student range.
West Chester has a large marching band, especially compared to school size, nice little downtown, and in-state tuition for you. Really wanted my son to look there.
Towson is a similar size and has half traditional downtown / half mall by campus. Delaware larger but the “Main Street” is more college-centric. James Madison and Miami of Ohio also fitting within your parameters.