Amazon offers the Stack-On In-Wall Security Cabinet, model no. IWC-11, for 30.83 with free shipping. That's the lowest total price we could find by $19. It mounts between 16" on-center studs and features predrilled mounting holes, removable shelves, and all-steel construction.

Update: Walmart offers it $29.86 plus 97 cents for shipping, however, it charges sales tax in more locations. (Free Site-to-Store pickup is also available.)