MidWay
The Ruger SR9 uses a proprietary magazine.
No, they do not use the same magazines.
It doesn't.
Try e-gunparts.com or Mec Gar
I paid $439 for mine at Outdoor World. MSRP is 525
Can't be answered without a DETAILED description of ALL markings, to include label on box.
I have seen very few used SR9 Rugers at my local gun shops. However you can buy a brand new one for around $360.00. That is a pretty good deal if they get some of the bugs worked out.
Magazine
Sturm Ruger still makes magazines for that pistol. They are the same ones used in their MK I variant and have a 9 round capacity. The subsequent variants, the MK II and MK III . They can be purchased on-line at the Sturm Ruger website, and are commonly available at gun shops.
You need the help of a gunsmith
Not recommended.
No, the magazines are not compatible.