Awhile back I posted a recipe for laundry detergent. Here is a great article on saving money with your laundry. The article has a similar recipe for detergent using bar soap instead of fels naptha. Even if you don't make your own detergent this article points out you probably don't need to add as much detergent to your wash for it to be effective.
P.S. I've looked for washing soda at several stores with no luck. An internet search pulled up the washing soda selling for a little over $3.00 on the Ace Hardware website. Amazon had the same product for $9.00.