They said 7.62x54mmR ammunition would always be cheaper than .308 Winchester.
Whoever "they" are lied from the get go. Or perhaps they are just young and never knew what the situation was back before the fall of the Soviet Union.
There was a time when Combloc guns AND their ammo were scarce, rare collectors items, with prices to match. The VietNam bring back SKSs were virtual wall hangers, no supply of ammo existed in the free world, other than what was captured or smuggled out. Mosin Nagants were a bit better off, because there was a limited source for 7.62x54R.
It had been commercially loaded in the US before WWII, but from what I can find, Remington stopped loading it around 1950. You could get ammo from Norma, but that was about it, until the "fall of the wall" (Iron Curtain".
Norma ammo isn't (and never has been cheap). MORE expensive than US made .308 Win sporting ammo, and way more expensive than 7.62Nato surplus.
SO, basically, from the 50s to the 90s, 7.62x54R was more expensive than .308 Winchester. Now, the wheel has turned full circle.
It won't be RIP for the Russian round, but it likely is the end of it being a bargain.