I have a 6' x 8' coup and I bought a 50lb bag of food grade DE over a year ago and still have probably half a bag left. I can't really remember how much it costs. I'd say Gardenstate was spot on for your coup size. I do the deep litter method and clean my coup just twice a year. After I clean out all of the old litter and sweep out the coup I usually dust the coup floor, base boards, perches, and nest box while it is bare. Then I fill the coup with 3-4 inches of pine litter and dust the top of that. After that I only add more when it looks like it needs it. That is usually if the oder is getting bad, litter seems damp, a lot of poo build up. I will occassionally redust the perches if I just scraped of a lot of poo. As stated by someone else it is good for drying things up. It may be good for bugs in the coup, but I don't know, I'ver never had any. So either I am just lucky like that or maybe the DE is taking care of it? I do believe in using it to keep the poo in the litter dried up. If I didn't use it I don't think i could go 6 months between cleanings. I don't dust my run as my hens free range and the poo in the run is not much and dries up on its own.