Hey! Depends how much plants your growing,, if just a few ( anything under 20). You should buy good soil ( fox farm, pro mix , wtv ). And buy some soilless nutrients , if your getting in to bigger numbers you should consider making your own soil, it's cheap and works great, find a companie that sells stuff for landscaping and or gardening, I'm talking the places where you drive up with a truck and they use tractors to load various soils,
Your looking for peat and compost ,,, I use 2parts composted pine bark 1part peat, I add powdered lime and control released fertilizer,, Works great and very cheap