I just made this last week! 1 cup Borax, 1 cup Arm & Hammer Washing Soda, and 1 bar of soap, grated. The remaining borax and washing soda will last me a year, easily, and I probably paid $14 for both of those.
After grating the soap, I put 1 cup of either the Borax or the Washing Soda in the blender, followed by the soap and blended well.
All I need is 1 tablespoon per load. It comes out to $0.03-$0.05 cents per load, and my clothes are just as clean if not more than when I was buying laundry detergent.
I still use fabric softener, so my clothes still smell like Clean Breeze. I doubt I'll ever give that up, I just love it too much!