It is a project, but not difficult for someone with basic woodworking tools and experience. I think I am into it for something like ~$300 CDN including the inkbird controller. I will post more about the design once I have it all sorted. Right now, the priority is to get it ready for my imminent crop.
Don't get me wrong, this thing is not, as far as I can tell, the complete equivalent of the Cannatrol. It does not have the ability to process at colder temperatures than the environment, and it will only work if the environment is lower RH than what is needed in the unit. Lower RH is no biggie with a small room and dehumidifier, but in warmer conditions, a warmer process temperature would have to be used unless AC was available. Neither of those limitations bother me because my drying environment is always drier, and can be easily made cooler than needed.
Bottom line is that as long as the RH control is good, and preliminary tests suggest it is, this thing should be able to accurately achieve .57 water activity in my entire crop in a single go. No bags, no burping, no overdrying, etc. etc.
My wife figured I was nuts before this DIY project, now she is completely convinced.