Hotel Charles
It won't win points for its looks (externally at least), but the staff are extremely friendly and helpful, the food in the restaurant is delicious, and the location is more convenient than it seems—just behind the hill, and close to the castle. There is a bus in front of the hotel that whisks you to Pest, too. It's the best of a string of low-priced, low-key options on this strip, which is also close to a conference center.