Found it!

Fels Naptha soap...I found it in the oddest of places, my local grocery store. 99 cents a bar. I figured out a breakdown of my cost per batch of laundry detergent

.37 washing soda
.33 1/3 bar of fels naptha
.00 borax (got a giant box from my brother for free)
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.70 per batch. 1 batch makes 2 regular (32 load size) bottles full and some extra. I am going to try this batch without adding anything. I will post how it goes. I am so glad I found the fels naptha and so cheaply and locally. Hooray!