I've made a lot of macaroni and cheese in my day, and I haven't always had the luxury of being able to afford milk. My go-to in that scenario is to use at least double the recipe's butter, and substitute the required milk with about 75% as much water.
It makes the mac and squeaky and it tastes.. not very good.
If they can't afford 1/4 cup (~60 ml) milk for a box of mac n cheese, they certainly can't afford half and half or cream.
If you're not in the US, get powdered milk, which is usually cheaper and for something like mac n cheese, it's plenty good enough. But in the US, powdered milk is more expensive for some stupid reason (probably something to do with dairy subsidies).
It is actually insane that powdered milk is treated as some obscure culinary ingredient in the US instead of, a nice and easy way to transport cheap long preserving milk. I get it doesn't hydrate perfectly but cooking with it is nearly perfect.
I have managed to find a single spice shop that managed to have it at a reasonable price. But powdered eggs is fricking everywhere and so much worse.
Well yeah, powdered milk is often twice as expensive as fresh milk, so no wonder it's relatively obscure here. Whole milk at Costco is ~$6.50 for two gallons ($3.50-4/gallon at the grocery store), the same quantity of Walmart brand powdered whole milk is $12.50 (makes 8 quarts, or 2 gallons). Non-fat milk is more reasonable (~$8.50 at Walmart for 2 gal), but still more expensive than liquid milk (~$5.50 at Costco for 2 gal; ~$3-3.50 at the grocery store per gal).
It makes no sense. Liquid milk needs to be kept cold in transit (we don't ultra-pasteurize), is heavy, and needs to be sold within 2 weeks or so. Surely it's cheaper to dehydrate it at the source and just ship the powdered product...
And yeah, powdered eggs is an atrocity. It's also way more expensive (like ~$0.60/egg vs ~$0.18/egg at Costco, or $0.19/egg at Walmart), and they taste so much worse, so there's really no reason to buy them either. At least in my area, I can own chickens for less cost than buying powdered eggs (but buying fresh eggs is cheaper than raising chickens). It just makes no sense.
The only reason to buy either powdered milk or powdered eggs in the US is for food storage.
Interesting read on the subject. I personally like having a mix that is egg-free, one can purchase "just add water" mixes.
...the fact was that fresh eggs produced superior cakes. Using complete mixes which included dried eggs resulted in cakes that stuck to the pan, had poor texture, had a shorter shelf life, and often tasted too strongly of eggs.