Quoted:
I've been told that the best way to buy oatmeal in quantity is to buy feed oats (for horses). Supposedly, the quality is of a higher standard than people oats for food. Ask some horse people, they can give you the straight story.
Oats used for horse feed is not oatmeal. It is either whole oats or rolled oats — oats that are run through the roller bars at the mill to crack the hull and gain to make it easier to digest. Sometimes oats are cooked to a mash and fed to horses that are sick or have digestive problems. Also, oats used for horse feed can be as good as oats used for human consumption, but there is no reason that it should be better.
Oatmeal is steamed and rolled. There are not all the many plants across the country that make oatmeal. Quick oats are just steamed (cooked) a little more.
For OP —
I searched for weeks to find an economical source for oatmeal in bulk, but didn't have much luck. I wound up buying 50 lb. bags of from Honeyville when they had a 10% off special and shipping was a flat $4.99.
FYI, Quick oats (usually costs more) can save some cooking time (about 3 minutes vs. about 15 minutes) but the texture is not as good as regular oats. However, if you are on the move and needing to conserve energy, quick oats is the way to go.