more frequently than not walmarts have had federal 1000 round packs in stock---i saw one at havana and arapahoe the other day--i think it was $379, but don't hold me to that price. that's about the cheapest you're going to get.

for the cheapest online, look at gunbot.net. SGAmmo.com is generally the best deal the i've found. Also consider freedommunitions, too.

Ammo still isn't as plentiful as it was last year, so i can't imagine you're going to get much of a discount in buying 10,000 rounds, which, in the greater scheme of things, isn't that large of an order.