You can use root tabs and be fine. But that amount will add up. Plus with sand you should use liquid ferts. The eco complete is probably the best choice and is $18 on petcos website. I bought it from them when it was $15 a bag. You could be patient and wait awhile for it. Or pay an extra $6 for convenience. I would go eco complete unless you are on a very strict budget. I personally have black eco complete and love it. My plants grow too fast!
Well I don't have a regular income and only have about $60 right now and I'd like to have 2-3 inches of sub and that would require more than 20 lbs so that'd be $40 just for substrate! I might wait till I get more money.