Ultima Replenisher alternative?

So as you all may know, electrolytes are a life saver when intermittent fasting. It’s pretty crazy how good you feel when you’re properly hydrated. I did a ton of research and discovered Ultima a few months ago. I absolutely love this stuff, but it’s just getting too expensive to be honest. When looking at the ingredients it consists of Magnesium Citrate, Potassium Phosphate, Calcium Citrate, Stevia, Sodium, etc. Would it be as simple as getting the pure powder form of these minerals and adding the exact amounts to 16oz of water and simply adding a stevia flavoring like Stur? I feel like it would be almost identical and I’d be saving a lot of money. If that’s something I can do, what company would you recommend for the powders? Recently, I’ve read that bulk supplements isn’t great and that Now supplements is much better. Thoughts?