I don't know if we have just "a small handful of companies" or not, but it certainly doesn't work as a compelling example for me of an anti-trust problem.
They are big and the easiest and most obvious to use and their prices are frequently good, but none of those are exclusively Amazon.
Citation needed on this one. Not my experience at all.
At four servings per pound that is 80 servings at $0.106 each.
Average yield of a rice plant, 10 grams.[1]
9071.85 grams of rice is 907 plants roughly.
That's less than a cent to cultivate, grow, prepare, bag and ship a rice plant. Let alone maintain the store where it is sold and pay the workers who sell it to you.
This is the miracle of the free market.
What price do you suggest is more fair?
[0]https://www.walmart.com/ip/Great-Value-Long-Grain-Enriched-R...