I can't find the biobizz light mix either. Instead I've tried using light warrior instead on my first half mix and on the second half mix I did I threw in a a bag of coco. 20%coco-80%roots soil. I did 20 plants with each half batch, so I'm guessing a full batch will yield enouph to do about 40-45 plants in 7 gallon pots. Remember the mix is good for one year, but the older it gets the more of it is needed per pot, because it gets weaker over time...
FYI ----> you did not include the cost of additional bags of soil for top dressing. Thats an additional 8-10 bags of Roots Organic. At the prices estimated by Marlboro47 (16$ a bag), your overhead is a bit high. Although could be worth it if canibus sells for a lot in your area.....