Borax is 2$, Arm &Hammer 2.50$ and Ivory soap is .99$ for 3 bars (but you only need one). I used lavender essential oil as a scent booster but of course you don't have to have that.
Next is the fun part. The original recipe I used called for grating the bar of soap but I discovered this really neat shortcut. If you microwave a bar of ivory soap, it expands almost 5x its size. It's really cool to watch. It cools off in about a minute and you can crumble it up into flakes.
Add equal parts Borax and Arm & Hammer Washing Soda and then add your soap flakes. After mixing well, I added 20 drops off lavender essential oil and mixed again.
I keep my detergent in a cereal storage container and it lasts for months. One warning.. It does not suds up but that doesn't mean it's not working....
So there you have it! Homemade laundry detergent for around 4 months or longer for about 6$!