I've been making our laundry detergent for about three years now. It's CHEAP and not difficult. I generally wash three to four loads of laundry a week and one batch of detergent lasts just under six months. My recipe is adapted from The Frugal Shopper, she has a couple of different recipes if you want to check them out.
3 quarts Water
1 Bar Fels Naptha Soap, Grated
1 Cup Arm and Hammer Washing Soda
1 Cup Borax
5 Gallon Bucket
1 Quart Hot Water
Mix Fels Naptha soap in a saucepan with 3 quarts of water, and heat until dissolved. Stir in Washing Soda and Borax. Stir until thickened, and remove from heat. Add 1 quart hot water to 5 gallon bucket. Add soap mixture, and mix well. Fill bucket almost full with hot water, and mix well. Set aside for 24 hours, or until mixture thickens. Mix the following day. Use 1/2 cup of mixture per load.
You can add essential oils to this, I've used extracts (from the kitchen) with limited to NO change in the scent. You need to make sure that you pre-treat stains, especially ring around the collar. This works well in all heat settings. I always use cold. There is no perfume scent or suds but it does a good job cleaning.
Occasionally, I will wonder if it's really doing a good job, and I use someone else's detergent (like when we're visiting family) and their stuff never does a better job. I sometimes want this to be better than the stuff that you buy in the store, because I made it, but the truth is that it is just as good as the pre-made detergents.
I have been able to find the ingredients at Kroger's, some at Meijer and hardly ever at Wal-mart. Fels-Naphtha is a bar with a white label, green and yellow detailing. You can also use Castille soap for this or ANY bar soap you happen to have on hand. The Washing Soda is found on the laundry aisle, upper level and it looks like a HUGE box of baking soda. IT IS NOT BAKING SODA, they can not be substituted for one another. And the Borax comes in a teal colored box with a team of mules on the front. If you can't find them at your store, you can find it at SoapsGoneBuy or at Amazon, though I can't recommend buying from Amazon as the cost is OUTRAGEOUS!
You can also just mix the dry ingredients and use them, I believe it's a tablespoon or two per load. This travels great (think camping!). We don't use fabric softner, the washing soda helps make sure the clothes are not to stiff.