Would depend a lot on where I was staying, how much I eat and how frugal I planned to be, local transport costs, and how much attractions cost. For example, Scandinavia would require, for me, at least $65 per day for hostel, average transport card, inexpensive late lunch, supermarket for snacks, 1 museum or major sight entrance daily, misc. sundries, but no alcohol. Additional costs for onward travel within Scandinavia, at least $30 extra for each onward trip. If I planned to camp, plus used a student ID for any discounts, I might be able to save a bit more.

In general, Scandinavia, Switzerland, and the capital cities are most exensive; eastern and souther europe generally less-expensive.