I always knew currency exchange at the airport was a bad deal, but I never really calculated it out -- I just tried to avoid it.
I was passing through Haneda airport last night, and had a stack of Chinese RMB I wanted to sell to get Japanese Yen.
The rate was 15% lower than the market rate. That's just one way. The selling Yen / buying RMB rate was similarly crazy.
To exchange $650 of RMB for Yen would have cost over $90.
That's nuts. You can get 1% or 2% at banks sometimes. A credit card with no foreign exchange fee (all Capital one cards, high-end Visa Signatures and AMEX cards) means you're getting 1% or 2% off the market rate. Worst-case scenario, you can et 5% pretty easily.
15%? It's nuts. Never ever change money at the airport if you can help it. You probably knew that, but it might even he worse than you thought it was.