We have traveled extensively in Europe and it goes without saying that your travel costs will vary, depending on the city and country.
For example, Florence is less expensive by far than Venice. The cities are in the same country, but the nice 4 star hotel we had in Florence in 2010 cost less than half the three star Venice hotel where we stayed.
We visited Portugal a couple of months ago and had wonderful accommodations in a top five star in Lisbon for 200 Euros, then a fantastic Bed and Breakfast in Porto for 95 Euros. Then a recent trip to Denmark we found everything more expensive. Hotels, taxis, meals, and tours were all expensive. A beer in Norway was $10 while one in Portugal may be 1 or 2 Euros.
Budapest is not an expensive city. Paris and London are more expensive, but you can find modest accommodations. Check out Rick's books or Kayak.
We are planning a drive tour of Britain next year and I have been researching B&Bs or small hotels near the city centers of several towns and cities we are going to visit and I have found accommodations from 50-120 GBPs per night. For Britain, I would plan on minimum of 100 GBP per night. Meals are expensive in Britain, but if you are in a B&B that covers one meal and you can skip lunch or have a snack and then only have the cost of one meal per day. Plan on $100 per day for food, which would include a beer or two. Tours are another matter. If you study your sights, you can DIY, but sometimes you need to pay for admission to some sights as well as a tour. Suggest adding another $25-50 per day. Transport is a factor. Taking the METRO in Paris or the Tube in London is pretty reasonable and easy. Just watch for pickpockets.
If you avoid the expensive hotels, I would plan on $300 per day, with more for expensive tours.