Once upon a time, a few months ago, I ran out of my store-bought “professional grade” brush soap. I had a bar of ZOTE soap around from when I was experimenting with making my own laundry soap, and decided to try it on my brushes. The soap worked great, especially on synthetic brushes, but was a little drying on my natural brushes. The ZOTE soap has a higher fat (Sodium tallowate) content than your typical bar of bath soap.
I decided to experiment a little since a huge bar of soap ZOTE is only 98 cents in the US. Before throwing away brushes with dried paint, try soaking it in ZOTE soap overnight. You can also use this soap to wash off major part of the dirt and use a more expensive soap at the end, to save some money. Got paint on your clothes? Rub ZOTE soap onto the spot before washing. I have also seen liquid pink soap sold in a small bottle for almost $5 at the art store. As an artist who paints almost daily, every penny counts when it comes to buying materials and supplies. I decided to show how I make my brush soap cleaner in a can:

Ingredients:
1 Bar ZOTE soap (pink or white)
2 ½ cups of water, or as much needed to barely cover soap
1 Tablespoon of safflower oil, coconut oil, or olive oil. I like safflower oil the best and, on its own, makes a great conditioner for your brushes.
1 reusable plastic tub, or can
Optional: 4 drops of lavender essential oil (used in many professional soap cleaners)
Note: ZOTE soap is drying on the hands, so make sure you rub a few drops of oil (not essential oil) onto your hands before handling.
Step 1: Chop up the ZOTE soap with a large knife–I believe you can get this already shredded in some places but it is fairly easy to chop.

Step 2: Place in pot with water and set stove to low-med heat. Stir occasionally to prevent soap from sticking to bottom of the pot.

Step 3: Wait until the water starts to boil slightly and test soap for consistency. Soap should be easy to mush with a fork or spoon, like mashed potatoes.
Step 4: Pour out extra liquid onto a separate container, squirt, or spray bottle and fill the rest with water. You can use this liquid to clean up messes in your studio, on your kitchen counters, for laundry stains, or whatever you desire. Add water, as the liquid will firm slightly in the bottle. Here are some uses for ZOTE soap: http://www.happypreppers.com/zote.html

Step 5: Keep mushing and mixing soap together and mix in oils well.

Step 6: Spoon into a container, or can, and press down firmly. Swirl your dirty brushes into the soap and rinse. I like to use a can because the ridges can help gently remove paint from paint brushes without compromising the hairs. You can place in the fridge for an hour to cool, or use right away. Store like you would any soap.
If you give this a try, let me know how it works for you! I will continue to experiment with different oils and will revise and update if I find something that works better.
If you have any recipes, please feel free to share in the comments!