I decided to dig around some old boxes of books to see if I could find one that would make a good case. This one was the perfect size. It looks like I paid $1 for it at a used book store (probably John King). I had a little anxiety about destroying a book, but a quick Amazon search showed plenty of used copies available for around $3, so this is in no way rare. Guilt assuaged, I went to work.
I didn't take any picture of the construction, which was unremarkable. There are plenty of tutorials online about making hollow books, so Google that if you are curious. The only thing I did differently was I used wood glue instead of Elmer's, which worked really well. I then lined the pocket with felt, to keep the tablet snug and safe.
I feel like this does a good job of camouflaging the tablet, while also protecting it. This cost me practically nothing, and took about 45 minutes to make.
I also glued an insert to the front cover that basically says "I belong to a nice guy. That guy has a baby. You wouldn't want to steal something from a nice guy that has a baby, would you?". It then has a couple pics of my daughter and contact info in case someone finds it.