at&t iphone 5 locked

Hello everybody.

I live in Brasil and I bought an american at&t iphone 5 for a good price. Now I need to unlock it and as I am not an att custumer I need to use some unlock services. I saw that these unlockers are having problem with att, should I still try with them?
I remember that months ago I saw cheap prices for unlocking and now it is so expansive, where can I find better prices?
I am thinking about using this one: officialunlocks website, does anybody know or have used it? Can I trust?

Thanks in advance