I think they also want a letter from your embassy confirming you are a real person. The UK embassy wanted 2,800 baht or something in 2004 so I just said stick it and use an IDP. I've only ever been stopped twice in that time. The first time I knew the cop and he just smiled and said off you go. The second one was a bit stricter but as soon as I showed him my tax and insurance and my UK licence he was fine and just told me to stay in the inner lane. No tea money, nothing.