$5. Not much but not insignificant. I'd rather AT&T just not lock it.

Edit: I thought I had read $5, but now I can't find that source, so who knows.

Another commenter in this thread is also saying $5. So it appears your memory is serving you :) ... unless of course you read it from this thread, ha

According to Ars Technica, it's free:

> An Apple customer service representative told Ars that Apple SIMs are available for free at Apple retail stores.

http://arstechnica.com/apple/2014/10/att-locks-multi-carrier...