I have done 8 to 12 weeks of riding each summer, for the past 3 years, throughout Western, Central and Eastern Europe. I don't camp, I stay in simple hotels, and I budget USD $100 a day for everything - food, fuel, lodging, tires, the works.
Of that, I probably spend about USD $40 a night on lodging, so you can modify that number by what you expect your camping fees to be.
Switzerland is expensive for food, but has the least expensive fuel in Europe. Swiss youth hostels are also very good, and very inexpensive. You don't need to be a youth to stay in one, they are very family oriented.
The central and eastern European countries are less expensive than the ones to the west. The UK and the Scandinavian countries are, in my opinion, the most expensive of all places. Anywhere in former Yugoslavia is quite inexpensive. Slovakia is a delightful place and also inexpensive, same for Poland and Slovenia. The portion of Germany that was formerly the DDR is less expensive than the more urban areas in the west of Germany.
Hope this helps you.