I used a recipe I found on several different sites.
1 cup borax
1 cup washing soda
2 cups grated soap (~1 bar)
There were several different soaps that people had used. The most popular seemed to be Fels-Naptha and Zote. I was unable to find zote at any of my local stores. I found Fels-Naptha at Fred Meyers (in laundry aisle) for $0.99 and at Rosauers for $1.49 (with other bar soaps). The washing soda and borax were on the laundry aisle.
Cost breakdown per load of laundry
5 cents - My Soap. With the more "expenisve" bars it would be 7 cents a load.
12 cents - Ecos Liquid. This is the cheapest "green" soap I found
20 cents - Tide Original Powder soap
22 cents - 7th Generation Liquid soap
25 cents - Mrs. Meyers. Liquid soap
25 cents - Tide Original Liquid soap
28 cents - 7th Generation Powdered soap
30 cents - Method Liquid Soap
** Prices based on largest bottle available (ie cheapest) from Soap.com