Machusetts vacation?

My friend and I want to take a 4 day vacation to Machusetts. We want to go Whale Watching in Cape Cod, the witch museum in Salem and other fun stuff like that. We are not sure where to stay exactly we do not have that much money. Also how far away is each town from eachother? For example, if we stayed in Plymouth how long would it take us to get to Salem or Cape Cod?