With just a quick check I find 7.62 x 39 steel case ammo selling for around 20 cents per rd. with current jacketed bullet prices it's going to be hard to beat that price but it possible shooting cast lead if you want to go that route. I started out around 15 year ago loading for the X 39 in my SKS rifles to guard agents imports being cut off and they have been shortages a couple of times and you couldn't find ammo anywhere.

Back then I used Hornady FMJ, SP and V-MAX bullets that I bought in bulk for around 8 to 10 cents a bullet. Not much savings there but I had better quality ammo that I could tailor to my rifles and better bullet performance plus I didn't have to worry about shortages. When I started casting my own bullets and using different powders or lesser amounts for cast lead that gave me more rds. per pound I cut my cost down to around 10 cents per red which I can still load it at that price today.

Cast lead is pretty much all I ever shoot in my SKS rifle or any of my other firearms for that matter. My favorite powders for the SKS rifles are 2400, Reloader #7 and either IMR or H-4895. My favorite cast bullets are Lee .312" 160 gr. RF or the Lee .312" 185 gr. RN and a NOE .314" 155 gr. FN, all are of the gas check design. Those same three bullets also do double duty in all my Mosin rifles and the Lee 160 gr. I size down and shoot in my 300 Sav.

All my SKS rifle have .312" groove to groove bores but shoot .310" jacketed bullets or .313 to .314" cast lead bullets best. Personally I've never found a commercial or surplus 7.62 x 39 cartridge loaded with a .312" dia. bullet. Even if its not currently affordable to reload the X39 cartridge you can produce better quality ammo and you never have to worry about political winds.