For now I just use large tea towels to over my machines if they don't have a hard cover to go over them. For my quilt machine I have a towel over the backside where the thread spool is as I have a kitty that likes to pull on the threads and take off with them. Then I put one over the front side where the robotic tablet is just to keep the dust off in case its days or weeks before I get back to it. I also use Dollar Tree windshield shades to cover my quilt that's on the frame to keep any kitty that thinks it's a great place to snooze. So far it's worked for me and it was cheap. If it's going to be a very long time between uses, I'll use some flat sheets to go over the entire system as there was a time I didn't touch my quilt machine for almost 2 full years. Lots of dust can accumulate in that time when in the basement.
Someday I may find the time to make proper covers for everything but just not right now.