ohknacks- WELCOME TO THE BOARDS!
After you get the Eurail pass out of the way, hostels and general accommodations will take the biggest bite out of your budget. I stayed in private rooms quite a bit and it averaged about $30-$40 a night, overall, through western Europe.
If you stay in shared dorm rooms, the prices are much, much, cheaper.
Museums are actually fairly cheap. Get an ISIC(international student identification card) card and you'll get half off of all or most museums and castles in Europe.
Clubbing. This can be costly, so drink before you get there or limit your drink purchases, and you will save money overall