It costs pennies to the dollar over commercial synthetics, uses no petroleum byproducts, and is sustainable. It won't cause detergent buildup on clothes, cloth diapers, or your machine.
Who can benefit from this? Your wallet, those with sensitive skin or respiratory allergies, and of course, the groundwater.
Step 1: Ingredients
If you can't find Washing Soda and/or Borax at your local Mart, ask them to get it for you, or you can also find it at various online places like "soaps gone buy".
Note, this is not the same thing as Sodium Bicarbonate, which is Baking Powder. Sodium Carbonate, sold, as "Super Washing Soda" by Arm and Hammer, or as "Washing Soda" by other brands, is used in everything from swimming pools to wet-process photography, and can be mined in its raw form, from the ground. It's a natural Earth substance, but caustic, which is why it does a good job. So don't leave it on your skin or get it in your eyes.
I use Kirk's Castile simply because it's cheap (a buck and change per longlasting bar), easily available, contains no animal products and is never tested on animals, is made from Coconut oil, contains no strong synthetic fragrances to set off my allergies, and is honest, pure soap without synthetic detergents (which are all petroleum byproducts, did you know that?)
I find Ivory too soft, and because so much air is whipped in, you get less actual soap per bar, and I couldn't verify the ingredients to my liking.
But if you want a fragrance, you can pick up a bar of Dr. Bronner's soap and have your pick of lemon, rose, lavender, and more. Costs about $4 per bar last I checked, but still much, much cheaper than storebought detergent.
If you make your own soap, even better.