For the last two years I’ve been using a custom mix from Infinit Nutrition that was engineered for centuries, which contains maltodextrin, dextrose, electrolytes, caffeine, and a little bit of protein to fend off hunger on longer rides. I only use it on longer, more intense workouts. It’s about $2.00 - $2.50 per bottle (USD).
I found SiS Beta on sale for $1 per packet a while ago and tried some. That worked well, too.
I plan to mix my own once I’m through my current stock. Electrolytes and flavoring could be the most expensive part, though. I also haven’t price caffeine yet, but am interested in recreating my custom mix from Inifinit as closely as possible.
For indoor rides I mix as many bottles as I’ll need before hand. For outdoor rides I carry extra mix in zip lock bags in my jersey pockets. The snack sized bags perfectly fit one serving of the Infinit mix.