I made a batch yesterday....
1 bar of Felsnaptha (or other laundry bar like Zote, Castile etc.) soap
1 Cup Borax
1 Cup Washing soda (or you can use PH up for swimming pools)
1/2 Cup Baking Soda.
Grate up the bar of soap, yesterday I used my food processor to do this for the first time and it was super fast and easy. Mix in all the other ingredients and you're done. Use 2 tablespoons per load. It works out to 20c - 27c per load, depending on how much you paid for all your ingredients.
I purchased more ingredients at walmart at the following prices:
Felsnaptha = 97c each
Borax (76oz) = 3.36
Washing soda (55oz) = 2.77
Baking Soda (4 lbs) = 2.16
The cost per batch of soap for each ingredient:
Felsnaptha = 97c
Borax = 37c
Washing soda = 46c
Baking soda = 13c
Total of $1.93 for the batch
Cost per 2 tablespoons (load) laundry = 7c