Here is the one I tried:
1 tbsp Washing Soda
1 tbsp Borax
Add the washing soda and borax in the detergent spot, and about 1 tbsp vinegar to the rinser.
Here is the cost comparison:
Washing Soda (56oz, 112 tbsp): $5.99 ($0.05/tbsp)
Half box Borax (38oz, 76 tbsp): $1.49 ($0.02/tbsp)
Vinegar (128oz, 256 tbsp): $3.19 ($0.01/tbsp)
Total per load: $0.08
Compare that to buying commercial dry detergent such as this on Amazon. Each box is $23.80, which makes 250 tablespoons. For a load, which would be 2 tablespoons as in my recipe, each load becomes about $0.18.
However, this is on sale at the local Safeway this week for $4.49.
For 75oz, that's 150 tablespoons, which make each tablespoon $0.03, so that makes it $0.06 per load (2tbsp). In this case, it's cheaper to buy it on special at Safeway.
It's probably a wash (no pun intended!) as to whether making homemade detergent would always be cheaper for everyone, depending on where you buy detergent and what deals you can get, but it's probably always more environmentally friendly and less likely to leave bleach goobs in baby bottles. As well, the price of commercial detergent may go up without notice, but Borax and washing soda is less likely to do so. And probably I could get away with using half as much detergent if I wanted to, which would make the cost per use 4 cents.
Anyway, it's worth a shot!!
P.S. Am I off in my calculations? I flunked my math placement in college and got placed in Algebra 2, which I'd taken as a 10-grader, so I might be wrong. In my calculations, I used 1 tablespoon = 1/2 ounce. If I'm wrong, would someone please correct me? :)