My first trip to Europe was paid for my the medical products company for which I and my co-worker, were employed, in order for us to become familiar with how certain procedures were done differently over there. The majority of our nights were in hotels that are today, and probably were then, four-star hotels. I found the experience of staying at those accommodations to be culturally sterile. I once remarked that we could have just as well stayed in the Holiday Inn in Peoria, Illinois, and had them put up pictures of Germany in the windows. Everyone spoke English to us. The food was basically American. Everything seemed to be arranged so that we would not have to experience the foreign culture.
A year and a half later, I went back on vacation on my own dime. I couldn't really afford four-star hotels. I got Michelin Guide and wrote, using my high school German for the first time, to one star hotels in town for reservations. All of my travel was by train, and a few taxis. I ate local food in the local restaurants. I loved it. At that time I paraphrased my own version of Rick's "Wall" statement as, "if you stay in small, family run hotels and Gasthäuser, you'll have a better cultural experience, and you'll save money in the process.
I have always kept an accurate, detailed accounting of my German travel expenses using a spreadsheet similar to the forms I had to keep when companies were paying my travel expenses. In five solo trips between 2002 and 2012, I spent an average of 65 to 70 euro/day, solo, on- the-ground expenses (not including airfare to get there). That was less than $65/day when the euro was less than $1, close to $100/day when it was $1.40/€, but it was still an average of 65 to 70 euro per day. Of that I spent about ~45% (30€/day) on accommodations w/ breakfast, ~30% (20€/day) for meals, ~20% (15€/day) for in-Germany transportation, and ~5% for miscellaneous.
I never stayed in a hostel, always in a small hotel, Gastaus, Pension, or Privat Zimmer, almost always with ensuite bathroom. I never dumpster-dived. I often had one meal of a sandwich at the Bahnhof when on the go, but usually one sit-down, restaurant meal per day. I usually picked accommodations that were within walking distance of public transportation.
But most of my nights have been outside large cities. Again, I think that way provides a better cultural experience. Over half of the nights I've spent in Germany have been in towns under 10,000 inhabitants; 85% in towns under 20,000. This, I believe, keeps my expenses down.
Since 2012, for health reasons, I've only made two, three week trips, this time with a partner. Because we share a room, our accommodation expenses have been less than twice what I paid solo, but because we were more likely to splurge on dinner, our meal expenses were more than twice what I spent solo. Still, our daily expenditures, over 41 days, have about 70€/day/person.
I agree with Avi's not including air fare in his calculations, since someone flying from the east cost to Ireland would have less fare than someone flying from the west coast to, say, Greece. But, I don't agree with expressing the expenses in dollars. I've seen the euro/dollar exchange rate vary over 50% in the last 20 years. I spent a lot less when the euro was 90¢ than when it was $1.40, but that didn't mean I was smarter then.
Lastly, don't let the advertised number of days fool you. On every one of Rick's tours, the first and last days are partial days, less than half a day each. His "13 day", BO Germany tour is actually only 11 full days and two partial days that don't add up to a full day, so less than 12 days - I'll say 12 days, because it actually includes 12 overnight accommodations. Because I spend almost half of my daily expenses on overnight accommodations, I actually figure the nights of a trip, when I'm figuring cost/day, as days.