Actually, speaking as a regular English tourist, Hannover,is probably the cheapest guaranteed package for visiting football supporters.
Easyjet flight to Hamburg, train to Hannover, (walk to the stadium from the hauptbahnhof).
They average around 40,000, but the stadium holds nearer to 50,000, and you can get a ticket for about 25 euros, either from the main ticket office, or supporters selling outside the stadium for face value.
There's also a great pub next to the stadium called the Waterloo.
The last time I was in Hannover was the day that City beat Arsenal 6-3. I saw them recover from a 3-0 deficit to draw 3-3 with FC Nurnberg