It's easy (and inexpensive) to make your own laundry detergent in minutes. And you only use a tablespoon or so with each load. So it lasts a long time.
Shake to mix well.
Store in a sealed container that is properly labeled. Use 1 to 2 tablespoons per load.
NOTE: Since the effectiveness of any detergent depends greatly on the hardness of your water, experiment by using the lesser amount, and then increase as necessary.