your doing great then , 4cuft of promix here is 60 bucks plus tax.
Sounds like your off to a good start!
One thing to keep in mind doing full organics (if thats is what your shooting for) is to have a bottle/s of instant food laying around. (any ol chem....MG, peters, advanced, fox farm, ect....) As your plant gets older , you will watch your soil start to run low on food, you can always just repot them when they get to that stage but if thats too much work or you just dont want to , then you can add small amounts of chelated food to give them the instant food they want.