It depends on the caliber.
Common calibers like 9mm & .223 can often be purchased once-fired cheaply, or found on the ground at a shooting range.
Slightly less common calibers like .380 ACP & .45 ACP that you can buy bulk pack ammo for at Wallyworld?
Buy the cheap stuff & shoot it for the brass.
You can often buy it on sale loaded, almost as cheap as you can reload it with good bullets.
Really uncommon calibers like .218 Bee, .45 Colt, .44 Spl, 25-20 WCF, etc, I reload.
I buy a 250 or 500 quantity of new brass.
Buying loaded ammo to shoot up for this brass is crazy expensive.
rc