MMM, I have a Bushnell 4x32 on my SKS, an Armsport 4x15 on my Marlin 60, and a Tasco Pronghorn 4x32 on my Marlin 1895. The Tasco was the most expensive at a big $35.
Since you want to put one on a 9mm carbine, I'd say go with something basic. A gun like that isn't meant for tack-driving. 4-power should do you fine. That said, if you want to do varminting, you might want something a little meaner than 9mm.
You can get Weaver See-Thru rings which allow you to use your iron sights. That's the setup I have on my 1895 and it works great.
"If your determination is fixed, I do not counsel you to despair. Few things are impossible to diligence and skill. Great works are performed not by strength, but perseverance."
-- Samuel Johnson