I use http://ammoseek.com/ to find whatever I am looking for. It's has a bit more user friendly interface.I've never seen that ammo available anywhere for .25 cents a round. If you saw a deal that good, you should have jumped on it.
If you want to look for good ammo prices online, gunbot.net can be very helpful:
http://www.gunbot.net/ammo/rifle/556/
Like IronMonster, I also prefer the 62 gr XM855 myself, as I consider it to be a better self-defense round, and it is only a couple of pennies more expensive. Also means I don't have to adjust my scope between practice and having the rifle ready to use for protection.
.