I am certain Denver has a military surplus store. They sell them along with everything else you need to survive the playa environment. They may be listed under "Army Surplus", "Navy Surplus", "Army/Navy Surplus" or outdoor sporting goods, etc.
Something cheaper and just as easy as MREs (and *possibly* more healthy...that's a tough call) is instant potatoes with salmon or tuna and a can of green beans. Homemade "MRE" for less than half the price
Louise and I always have a few Heater Meals available for when it's too windy to cook. The Quick Meals page has other alternatives, as well as info on official military MREs and their calories and salt. Quick Meals will give you a list of a variety of food which can be prepared with no cooking or just boiling water. It's not all cheap, though - it costs to be quick.