Surprise, surprise: THE high season in Berlin is right over New Year. I really didn't know that. Most places are already booked and what's left has hiked up their prices, often doubled them. I was hoping to find something for up to 100 Euro/night for our family of 4. That price range hasn't been an issue for us travelling all over Europe in the past. But now I could use some more tips.
vrbo had only 4 offers matching in size and prize (did I make a mistake in the search???) and the answers I've gotten so far were negative. I tried www.fewo-direkt.de as well which has a lot of affordable options but no luck so far (still waiting for some responses). Hostels don't really work for us in as they charge by person and that adds up as well. And the Circus is full anyways. I tried a few hotels and pensions but no luck there (full or "special pricing").
My strategy so far is to cut our stay in Berlin by 1 or 2 days and stay longer in Leipzig where we can stay for free with family. Thus allowing for a slightly higher hotel/appt rate in Berlin but still need to find something ...