I saw koln play was 20e. Your mate must have had the best seats in the house.
Most I've paid is 30e at frankfurt, but bought it last minute. They had tickets for around 18e.
Been to around 6 or 7 different German grounds in last few years.
Each have:
Terracing
Cheap tickets
Cheap beer
Beer in your seat except away end
Singers at front with speaker phones