Well I personally believe that if you have a good soil source why pay for it?
for example.. I have huge pines behind my house & the soil under those things is amazing.
I just add i lil garden lime, worms, worm castings and about a cup of pearlite per/sqft of soil.
in a gallon pot I use about 1.5 cups. You want to roots to be able to grow & expand real easy.