Traveling Europe Cheaply - looking for advice

Looking to visit Europe (from the U.S.) for 2-3 weeks next December with a small group of friends. Trying to keep the trip as cheap as possible but still have a great time. Plan is to fly out on Thanksgiving to cut costs.

We're thinking of flying into Barcelona or Munich, maybe, and then getting a Eurail pass and just hopping around and staying as cheaply as possible. We're young and would be happy sleeping in hostels or whatever.

We're working with a limited budget (ideally sub 1500 USD per person, total; the cheaper the better). We know to avoid Paris and London if we want to be cheap, but not much more than that. None of us have spent much time in Europe so we're kinda interested in everything/everywhere that seems cool, including small/out of the way stuff.

We're fairly uncultured Americans, so ideally English-friendly places, though between us we have survival-level French, German, and Spanish.

Anyone have tips/ideas/places?