Antje: Do what I do. Check today's exchange rate.
http://www.xe.com/ With this knowledge you go down to the liquor store or Post Office and buy a money order. It costs between 35¢ and 95¢ depending on where you go. Make sure they sell international money orders, otherwise go somewhere else. There's no extra charge for international money orders and that's what you need when Filip goes to cash it in at his bank or they'll charge him for it. Buy the money order and then mail it to Filip in the Czech Republic. Postage was 80¢ the last time I did this. I just checked, it appears rates have gone up. It is now 84¢
Airmail Letter Post 4 - 7 Days $0.84
http://ircalc.usps.gov/intl_speed.asp?CID=10086&MailType=envelope&Pounds=0&Ounces=1 There's a link on the rates page about what can be sent to the Czech Replubic.
Ask Filip for the mailing address. When you mail the money order include your account number and handle with it. And put some neat stamps on it for Filip. :)

I haven't tried the customer service route in the United States. Seems like Eriisa has been doing it for awhile, it works well, and the postage is less for domestic mail.
http://brainking.info/service.html Customer Service link