You could try all the websites to get a feel for the prices 2 days in advance to begin with. Same day or even next day bookings are only possible by phone or at the airport, not online - my experience. You have to have a Saturday to Sunday in there somewhere to qualify for most cheap and cheaper flights, as most of us have found out when it was inconvenient. Without the weekend, prices rocket as high as EUR 1200+ as the airlines want to target business travellers. It depends on where you are as to which airline is cheaper or suitable. Occasionally you might get lucky with KLM, change at Amsterdam. Air France might be useful in an emergency, change at Charles de Gaull (the worst airport I have ever been to).
Cheap airlines appear to get more expensive, the closer you get to the date you want to fly. I recently had two situations where I had to find out quickly how to get back to the UK, but both times the emergency was over quickly and I did not fly. It certainly made me think of how I could get back quickly if my family needed me!
You might find
www.flug.de useful, but they don't include German Wings, Buzz, Ryan Air and maybe not DBA. To find out which airlines fly to your destination, visit the website, for example:
www.baa.com.