Success! I did Augusta +1 this morning using my first homemade mix. Recipe and costs are below, with links.
1/2 cup (60g) Maltodextrin
$24.50 for 57 servings
2.5 tbps (30g) Fructose
$22 for 90 servings
1 Nuun tab
$24.50 for 40 servings
I also got a digital kitchen scale and confirmed that the volume measurements equate to the weights above (i.e. 1/2 cup malto is about 60g and 2.5 tbsp fructose is about 30g).
Total cost per bottle is $1.30, with the Nuun tab being almost half the cost. As others have mentioned above you can use sodium citrate for electrolyte and add flavor (lemon juice, TRUE Citrus, etc) to cut the cost down even more.
The Nuun provided all of the flavor. I mixed it in 24 oz (750ml) of water and it was similar in sweetness and intensity to SiS Beta Fuel mixed in the same amount of water. My custom mix from Infinit Nutrition has caffeine in it, so I’ll likely get some Nuun+Caffeine tabs for those early morning workouts where I’m struggling to wake up.
I have some left over Precision Hydration sachets that I’ll also try instead of Nuun. These have a much more subdued flavor and might be good for longer rides where pallet fatigue could be a concern. They also have 17g of carbs versus Nuun’s 4g (not accounted for above).
EDIT: For simplicity, 2.5 tbps is nearly 1/4 cup, which is what I use to measure the fructose. The mix ends up being a little sweeter but you also get a few more carbs.