$7 but the inside of the steel has to have images too. There si no such a big price idifference between amarays and steels I mean in terms of factory price. The thing is if they work on a good desing and so, is OK to go for $10 extra, but the average price would be $7.
7 USD is fair enough as a difference. In case of something speciall (like embossing a steelbook, or applying something interesting design feature compared to the plain amaray version), reasonable difference might be more.