Actually, MREs aren't cheap, about ten bucks each at the commissary. You can get a slightly decontented version for about half that much, can buy singles or cases.
MREs are cheap to manufacture. Commissary are going to charge full contract rate, but look at surplus stores around Augest/September (end of the goverment fiscal) and you'll find cases of 12 going for $40-50, shipped. If you really want to save on groceries, get on the government auctions and buy you a pallet which is often $2 or less per, sometimes as low as $1.
To tl;dr on the economics:
MREs don't expire. As long as the retort is not compromised by oxygen, they will last indefinitely. In PRACTICE however oxygen will eventually compromise the retort and they are only required to last 10 years at ~40F, but the actual life will depend on storage conditions and handling.
Thus they have a manufacture date and an "Inspect" date. What is suposed to happen is on the inspect date, there is to be a random inspection of some of the MREs to check for degradation. This takes time and effort and the government has already committed to the manufactures to buy a certain number every year. So what will happen is a small number of batches are inspected to retain the capability, but 99% of all MREs hitting their inspect date will instead be auctioned off. This is the difference between a "new" $10 MRE (will last 10 years at 40F) and the $3-4 "on sale" MRE (already 3 years and stored at lolidk degrees C ). They won't be bad, but you're looking at only 3-5 years of "for sure" shelf life.
I keep a couple cases as "Oh shit" meals and usually just try to chow through one per month and order a new case every year so aging isn't an issue for me. If you are buying them to toss into your lifeboat or in your trunk, you will probably need to replace the $3 discount MRE more often than the $10 "new" MRE.
