Juha,
Since I am taking at least two flights on two separate airlines the oversized baggage cost could be as high as $150 per flight, or $300.
Part of the problem is that I'm used to U.S. pricing. A decent bike from Wal-Mart costs less than $150. A decent-enough folder costs less than $300.
If I wasn't taking two separate flights I would just bite the bullet and pay $150 to take a cheap Wal-Mart bike over and then abandon it at the end of the trip. But I'm not willing to spend $300 getting a $150 bike to Europe.
I don't know if I can buy a cheap folder in Heidelberg or not. I can certainly try. But I only have 24 hours on the ground there, so I'm going to need to start bike shopping as soon as I step off the train.