I buy a product called Kellogg's Patio Mix at HD--my HD does not carry the ProMix. The Kellogg's is certified organic, I have had great luck with it, and it is quite inexpensive. If you are going to grow organic, everything is going to have to be organic. Do not buy any soils like Miracle Grow that have moisture crystals in them or says that it feeds for x number of months.
You are probably going to have to order nutrients online if you do not have some kind of shop around where you live. Cannabis has pretty specific nutrients needs and these needs change depending on what stage of growth the plant is in. Things like Miracle Grow fertilizers that you buy in the big box stores is not a good fertilizer. You are going to want something formulated for cannabis.
Tell us about your space--size, lighting, ventilation and such. While you can do this on a budget, it is imperative to have enough lighting. While there are things you can scrimp on or DIY, trying to scrimp on lighting is one of the biggest mistakes new growers can make.