Someone on this forum wrote out what is known as "the recipe" if you search you might find the thread. But here is what they shared about making your own soil.
It consists of:
1) Silica- I always recommend soluble silica like PowerSi or Grow Genius. If you are in a pinch, you can use potassium silicate, but you have to keep an eye on the pH.
2) Jacks Classic Hydro, Calcium Nitrate and epsom salt- This is your base fertilizer. It is 3 grams Jack’s, 2 grams calcium nitrate, 1 gram epsom salt per gallon
3) Fulvic Acid- This helps prevent pH problems and plant stress and gives organic taste and smell. There’s lots of watered down additives out there, but I recommend Mr. Fulvic because it Is a concentrate and has fulvic, amino and organic acids.
The quality and yields are phenomenal. Depending on what quantities you buy, it can be $0.06-$0.10/gallon.