You get to another level of cost savings when you buy in bulk. Loading a few hundred rounds saves some, but even better when you can buy 2-4 kegs of powder and spread the hazmat fee over that instead of just one, or a few pounders. Same with bullets. Hornady and Nosler usually offer big discounts for buying 600-1,000 ct instead of 100ct jacketed bullets. Cast bullets are way cheaper by the 1,000. You can often get flat rate shipping of $12-$15 for up to 70 lbs. Primers are usually cheaper by the thousands than the sleeve. And if you buy them when buying powder often the hazmat is spread over all of it. So it makes a lot of sense to buy in as big a qty as you can afford if you want maximum long term cost savings. Side benefit is have lots stockpiled against a future supply drought/buying frenzy, or disaster situation where resupply may be along time coming.
Up until 1994 I thought 300 rds of a cartridge was a lot. Usually had 100-200 bullets on the shelf, and a few pounds of powder and a few sleeves of primers. Just enough for the next couple of reloading sessions and then down to the sporting goods store for more. After the AWB and resulting supply challenges I upped my inventory to enough components to reload 1,000 rds of each caliber. Then when I saw what was going to happen in 2008, I started in 2007 building up inventory for at least 5,000 rds per main caliber and 2,000 for the less used. I had to invest in much more storage capability and equipment for that as well. But all through the 2008-2016 drought I never ran out and even hosted many family shootfests supplying several people with lots of ammo. I did start to get nervous in 2016 and cut back the all day shootfests and did more focused and less quantity shooting. And I wasn't even competing! Those guys can go through 3,000 in a week.
I don't think you can have too much ammo. Just when you think you have enough, something will happen to make you realize you could have used four times as much. But I would be selective on calibers. Not all calibers need to be stocked to the same high levels. Rather than stocking 1,000 rounds of ten calibers, it would be better to stock 3,000 of two of them and 500 of the less important. May main calibers are .223, .30-06, 9mm, .40S&W and .22LR. I have more than a dozen secondary and tertiary calibers. But you have to scale it to your budget and "needs." Probably want high volumes for defensive calibers and less for hunting or "just fun" calibers.