I use this keyboard case. Got it for $15-20. It's no slick magnetic snap case but neither is it one hundred dollars. Works fine for me. I'm guessing a lot of other cheap keyboard cases would work just as well or better.
Mine is a little tight in the corners so I do cringe a little when zipping it up, but I've seen no noticeable wear in the last year so probably not an issue.

How much do you want to spend? I got this case from amazon, it bulges a tiny bit but not much. You’d have to double-check that it’s the correct size lol, but something like [this from Etsy](www.etsy.com/listing/171657363) might work