I buy extra ammo and mags when I order ammo. Not a ton, like a savings account - 420 rounds for me, 120 rounds for the pile. 2 new .308 mags for me, 2 new 5.56 mags for the pile. When I'm in wally world I poke my head into the ammo area, buy a box of this or that or this and that..
For me - it's not spending $1000 on ammo, I make little payments, maybe I pay a little per round, but doesn't require lots of consideration that way either.