I found these simple ingredients at my nearest Walmart in the laundry soap section. They were surprisingly easy to find, and extremely affordable:
Fels-Naptha Soap Bar ($0.97)
Arm & Hammer Super Washing Soda ($3.24)
(You will also need one 5 gallon bucket with a lid - I also found this at Walmart for a total of $3.71)
(You can also add 1-2 drops of essential oils per 2 gallons once it has cooled)
I was very pleased with how well this soap cleans. The last time I bought laundry soap, I got the cheapest one I could find (and it doesn't clean at all!). With this recipe, the clothes come out smelling clean and they feel clean too.