My first foray into the world of fabulous and frugal DIY recipes was powdered laundry soap. I actually got this from a friend of mine.
Ingredients: 1c washing soda, 1c Borax, 1 bar Fels Naptha
You need to grind up the bar, or shave it. Sometimes it helps to put the bar in a freezer for a bit. Mix it all together and you are good to go. Additional notes: I try to dissolve the soap in the washer before I put my clothes in, just seems to work better that way. This is also a low suds soap so it works in the HE washers.
Here is a website to help give a good break down in cost: http://www.diynatural.com/homemade-laundry-detergent-soap/