Arsue Dual Layer Hybrid Case ($6)
If you're looking for a cheap case that's more durable than a typical case you see every day, consider this one. Dual Layer hybrid cases are another popular choice as they aren't too thin, not too thick, and usually cost under $10.
The Arsue dual layer hybrid is exactly that. A case that uses a soft TPU inner shell, but then covers the outside of the phone with a hard polycarbonate plastic. Giving you a relatively thin design while retaining the strength of more expensive cases.
One of the best aspects of a dual layer case like this one is the hard plastic doesn't cover the corners of the phone. Instead, the impact-resistant TPU material sticks out and is a little thicker on the corners. It's also scratch-resistant and has a soft textured rubber back for a better grip.