Have you considered Space Buckets? https://www.spacebuckets.com/ See also: https://www.
reddit.com/r/SpaceBuckets/ They claim the total cost is about $100. I was going to try space buckets but then I built a hidden room behind a closet, added a 63"x32"x32" tent, carbon filter, etc and my costs are just under $700 but that includes $180 in hidden hinges for the secret door. I am thinking of setting up some space buckets for germination and vegetation then using the hidden closet for flowering. Knowing the children won't find the hidden closet is a comfort but surpasses "cheap." I would highly recommend looking into Space Buckets.