Perhaps you are over-thinking things a bit.
3 year supply sounds like a lot of grain to keep in storage. I would think you might target no more than a year at a time, perhaps give yourself a few months extra in case prices fluctuate, or you need more or less grain.
I'm seeing a number of small silos around the Northwest for not too much. Keep in mind that many silos are outdoor stand-alone structures that are poorly insulated. Both ground level and conical silos. So, perhaps your barn with nitrogen is way overkill.
Grain Silo
Grain Silo
Silo
medium size grain silo
14 by 9 silo
SILO FOR SALE
As far as Augers, they vary somewhat. Not all prices are listed.
A bunch of auger parts, price not listed.
grain auger & grain piping
This one apparently came from a grain truck... it might be the best for adapting.
Seed Auger For Sale
One on wheels.
Grain Auger 33'
Another.
Hay elevator or grain auger
Bin & Auger?
GRAIN BIN & AUGER SYSTEM
I didn't see a lot of grain/feed trailers, but a few.
Case feed wagon
A & L 425 Grain Wagon
old feed wagon
My JD 602 fertilizer spreader was about $300. Like I said earlier, it would make a good bin trailer for a little over a ton of just about anything. I assume more will show up sometime.
Roller Mill.
I assume this makes stuff like rolled oats. Probably a lot lest dusty than our old hammer mill. I don't know about the feed quality for different animals.
Grain Roller Mill
Couple of old Hammer Mills, I think.
john deer grain mill for sale
grain mill for sale
Hammermill
Hammermill Is there a mill in there somewhere?
I drove from Eugene to Pendleton a few weeks ago. Too bad I didn't snag something on the way to bring your direction.
Assuming you're thinking a year or two ahead, have patience, and keep looking. You will find the parts and pieces you need at the price you're looking for. Perhaps some of the building and configuration could be done incrementally as you experiment with different ideas.