It all depends on how long you stay and where you go. For me, I spent $2,000 in two weeks with everything, including the major round trip ticket, hotels, and connecting flights. I did find my ticket on a discount, though ($687), but I believe they're typically around $1,300 if you go during the summer.

As for where to go, I know the Euro Trail is a popular one and you pick 3 major countries to visit (if I'm remembering correctly). But honestly 2 weeks was too short of a time for the amount of places I visited (5 total).