I have not found unlock codes for the 8220 for less then $17. My experience after trying 5 different unlock vendors is that most return "not found" which means that the code is only available directly from RIM. Horizon Wireless was the only one able to get the code for my 8220.
The best bet is to contact T-mobile international services and request the code. Explain the situation, you have nothing to loose. There are posts on various forums reporting success even though they were not customers.