Anytime is a good time for more ammo. Prices are low right now but for most calibers they're not going to get much lower. From an ak perspective MOST milsurp is now banned from import with the ban on 7n6, 7.62x39 with the shank was already banned before that. If it were me I'd stock up on 5.56, 5.45, 7.62x39/51/54r while there's some decent prices still. An above suggestion about stocking up on mags is a good one as well. Do you have enough magazines to last you from now on? Pistol calibers as well are cheap right now.
You don't have to go crazy with it from a pricing perspective, one of my buddies spends $25 a week on ammo, he rotates through .22, shotgun, pistol and rifle calibers, etc and he's built up a pretty impressive pile of ammo over the time he's been doing it.