You can pick up surplus (and old) Mosin-Nagants for well under $100. But why go cheap? You can buy a fine first quality rifle for $600 or less. I have a Remington Model 700 chambered in .270 that I use for hunting large game. That model is reasonably priced and is very accurate. I like mine a lot. But a SHTF scenario might call for something other than a long distance weapon. There’s a lengthy post that can be found at various places on the Internet (including this site) by an Argentinean who found himself in survivalist mode when the Argentine economy collapsed in 2001. His advice: forget long distance shooting. Your challenges when TSHTF will be up close and personal—not at 200-300 yards or more. After I read his account, I decided to start stockpiling ammo for my new favorite weapon: a Ruger Mini-14 Ranch Rifle chambered in .223. Not exceptionally accurate beyond 100-150 yards, but compact and reliable, and can push bullets fast and furious, and there are thousands of custom options available including high capacity magazines.
That mini 14 you think is so reliable is notorious for jamming with anything but fmj factory loads.