I use Tripp magazines in all my 1911s (.45, 9mm, 10mm) and pretty sure it's the same price no matter what caliber. Only difference is if you get an 10rd extended magazine which is a little more. The Tripps have worked very well for me in all my Kimbers.
Can't speak for the stainless 9mm, I have an Aegis Custom II that I made changes to and use in IDPA. Magwell, carbon fiber grips, more "standard" thumb safety and magazine release. Been very happy with it.