iPhone 4: How much does it cost to unlock an iPhone 4 using a Canadian Operator?

I don't live in Canada, and Apple products are restricted in my country. Therefore, I need unlock my iPhone, using BELL (a Canadian network operator) because this particular phone is set on this particular Canadian operator. I've been told that it has a legitimate international price to get this unlocking thing done and I want to know what the price is.

Thanks in advance