Some more authentic Steinbrenner balls. These were offered for sale in the Yankees Team Store.
Here's a ball signed by Steinbrenner and Brian Cashman; I took this photo in 2006, and you'll see the price was $400...
Here's a single-signed ball photographed in 2008, the price wasn't listed otherwise I'd have noted it at the time...
Finally, here's a single-signed ball displayed as part of the Ball Wall in the Yankees Museum... this photo is from 2009...
Unfortunately, all of these baseballs appear to have been signed with a Sharpie.