This is designed to be the simplest, thinnest cardholder that can also hold paper money. It is designed to hold around 4 cards plus a few bills.

I recommend printing standing on the thin flat end but you may have better strength printing flat. You may also need to mess with the scaling if your prints tend to shrink significantly.

I made a much thicker version years ago with a sewn on cloth pouch to hold money and USB drives but I realized it made more sense to attach the USB drive to my keychain and use a cardholder, but I wanted to be able to keep paper money on myself as well. The idea with this is that you have a thin fold of paper money underneath the cards, to keep them tensioned in the holder. If you don't want to carry paper money, a small strip of other paper, folded a few times, will work just fine.

I made it in Tinkercad.