Thumbs up [Q] Sony Xperia M Network Lock

Hello There

I am new to this group and joined this forum to seek some advice from you guys. I have bought Sony Xperia M (Boost Network, powered by Telstra) in Australia. However, the phone is network unlocked. The phone cost me $200 and now i am visiting my hometown for vacation and to use phone with my country sim, I need to get it unlocked. I called Boost mobile and they said that they will charge me $100 to unlock the device. Can somebody guide me from where I can get it unlocked for cheaper amount, although the cheapest option I found is $25. Or If somebody can help me how to generate network unlock code from IMEI number.