I just went through this process and wanted to give everyone a heads up.  

First, they are no longer in Van Nuys, CA.  So it will take longer to send the payment as they are in Amsterdam in the Netherlands.

Secondly they ask for a post office international money order.  No can do!  The post office does not offer an international money order for the Netherlands.

They will also accept a Western Union Money Order.  I could not find a currency exchange near me that sells them.

They finally agreed to accept a casher's check from a MAJOR bank.  (breathing a sigh of relief) lol

I had to options to send it quickly from the post office.  Priority is about $6 and delivery is 4-5 business days.  Express is about $29 and delivery is 3-5 business days.  Needless to say, I went with the "priority."  Not sure 1 day is worth $23.