@Never Give Up - One option is to mix up your own electrolyte mix. You just need a source of sodium (e.g., table salt and/or bicarb) and a potassium source like potassium chloride (ingredient in salt substitutes). Then you mix them in water. It's a bit less convenient to use measuring spoons instead of just opening a packet but it is way cheaper.
Optionally you can add some sugar source. I use powdered dextrose. This may help some people absorb the salt better. Here's the recipe that I use:
This is fairly close to the WHO recipe for electrolyte replacement. I think it can be adjusted to suit the patient but definitely check with a doctor. Although it seems like this would be better than so many liters of plain water for someone with POTS and/or NMH.
Most folks on the forum have said that they don't need any sugar and it does not make a difference for them. But it does seem to help me for some reason whether it is absorption (I'm drinking it on an empty stomach and often skip dinner completely) or something else. It's a pretty small amount (1 tablespoon = 45 calories = 12 grams carbohydrates) and it seems to be metabolized differently from sucrose or fructose.
I was drinking the clear, unflavored Pedialyte before I switched to mixing up my own. Since that was working well for me, and it includes dextrose, I tried to find something close to the same when I looked for a recipe.
Hope this helps.