If you're running low, I would get maybe 2-3 cases (more/less depending on what you 'normally' have). I haven't watched 7.62 x39 pricing that much, but I've seen Tula and some other brands on sale here and there online. Would have to go through Kaleo Arms, but always a decent option.
I've mostly been watching prices for 5.56 and 9mm. I haven't bought in a long time, but it's good to see a steady decline in prices for both of those. 9 mm still in the 0.30-0.33/round range, which I think is still too high for me to buy, but likely the "new normal". I'll likely reload more than buy at that price. Different for 7.62x39. I don't shoot my AK that much these days. I'd like to if I had more ammo, plus open shooting bays.