I buy the DE in 4 lb. bags at Home Depot or Lowes. It's $8-9 a bag.
I just sprinkle it over the leaves and put some around the stalk so the 'wigs have to crawl through it to climb up the plant. The strainer might be too fine. I use a bottle with a shaker top. It's very fine powder and clogs easily. So I use a top with bigger holes like on the jars that Parmesan cheese comes in. I have a hard time believing the coarseness of the powder tears their bodies as claimed. I'm more of the belief that the silica in the powder dries out their insides when they eat it on the leaves. Even with well over 100 plants, a bag lasts me a year or more.