I started making this when my husband was in graduate school. It was cheap and easy. I really stuck. I only have to make it every 9 months or so. My kids think it is fun to make. I can find everything at the grocery store for less than $25. Or a kit is available on amazon. You can add essential oils for a custom smell.
Homemade Laundry Soap
1 box of washing soda
1 box of borax
4 bars of fels-naptha soap
Grate the bars of soap. Smash the lumps in borax and washing soda. Mix together. Store in an air tight container. I store mine in an old icing bucket.