Most any firearm enthusiast knows that 7.62x54 is often cheap to find
7.62x39
If you assume that the OP was asking about only surplus ammunition, .22 LR and .22 Short has been available as surplus many times over the years. (Surplus training ammo.)How is .22LR and .22 short milsurp?
...Then it isn't about a rifle or ammunition.Cheapest Milsurp Caliber that isn't 7.62x54r?