So I didn't have enough money for a ticket and missed an opportunity to buy one last week.
Seems to be marginally cheaper to buy a trip to Dusseldorf and take a train to Cologne than fly directly there. And it looks like a short train ride is necessary to get to Oberhausen.
Fly in Thursday 7/18 (festival is 20 and 21st) Fly out Tuesday 7/23.
Fly in Wednesday 10/9 (festival is 11.12.13) and fly out Tuesday 10/15.
Get one round trip flight Origin -> DUS 7/18/2013 and DUS -> Origin 10/15/2013
Get second round trip flight DUS -> Origin 7/23/2013 and Origin-> DUS 10/9/2013
And split the tickets to match the dates above. I was trying to save money on the first trip (without insane layovers).
I suppose the overall cost could or would drop due to the amount of time before the second festival.
I think that guy in the movie "PI" actually tried cracking the airline ticket pricing patterns and that's why he really went crazy.