rates

I'm assuming you're talking about hotel rates:) A varies at bit, but for most places the entire month of September is still considered "high-season". Even though there won't be as many Americans around after labor day, there are still plenty of tourists from other places around the globe. October is more the shoulder season when rates starting coming down. One thing to keep in mind is that airfares from the US to Europe will drop after labor day, so that might mitigate the higher hotel rates.

Prices in family-run B&B's and apartments tend to be very low in Germany year-round, including September (they often go UP a bit in winter months to cover heating costs.) For hotels, commercial sites like Orbitz and Booking.com are good sources for special deals.

Websites for the hotels, which you can find if you use the town websites, www.townname.de (or ch or at) will usually show you the rates for high and shoulder season (Haupt or Neben Saison), along with the dates.