I used to be in the restaurant business as a cook. Your most cost effective way to grind dry oats would probably be an inexpensive food processor. If you don't already own one, you could buy one at WalMart. If it doesn't work well for you, you can always return it! I found a "Grain Mill" for $260 at
http://www.pleasanthillgrain.com/index.aspx#Nutrimill while searching for a "Burr Mixer" (the commercial version). Kitchen Aid mixers might work too if you had a grinding attachment for it like a Hobart Mixer in a restaurant would. I'm pretty certain that a food processor would work better than a blender. Good luck.