depends how much u need. Go to home depot or where ever your closest nursery is get a bag of top soil or organic potting soil. Mix in about 25% sphagnum peat moss and 25% perlite (rough estimates will do fine). You can add dozens of other amendments just Google organic soil recipe or w.e. I'm using the soil/peat/perlite along with dehydrated cow manure, alfalfa meal, bat guano, worm castings, peace of mind fruit +flower and dolomite lime to maintain ph.
Of all this the most important is probably the manure, worm castings, and lime. But the peace of mind by fox farms has alot of the essencials in it, its like perfect super mix of additives for under 10 bucks. Ingredients: Feather Meal, Bone Meal, Hydrolyzed Fish, Fish Meal, Fish Bone Meal, Alfalfa Meal, Sulfate of Potash Magnesia, Blood Meal, Bat Guano, Rock Phosphate, Kelp Meal, and Gypsum.