OP didn't ask for your opinion on whether Gatorade is or is not priced affordabley. He asked if anyone had anything cheaper. If you don't have a suggestion, I'm sure we'll all live if you just move along without sharing your dumbas* opinion.
Anyways, I make my own because I can make it to perfectly suit my needs (I'm a cyclist so my needs are a bit different than yours would be). Although mine comes out more expensive, you COULD make it cheaper than Gatorade if you wanted. Tons of recipes out there but the simplest thing you could do is water, salt and sugar.