i-Blason Clear Halo Series
Another good option comes from the guys at i-Blason, who makes some pretty great cases. The listing on Amazon states this has a 3H hardness rating, meaning it likely will be very strong. Many cheap TPU cases get scratched pretty easy or start to wear and fade after 6 months to a year. That shouldn't happen with their case.
It's likely made out of a hard polycarbonate plastic shell, and completely clear, but the listing doesn't fully explain. Either way, just know this is a durable clear case that won't scratch or discolor and is pretty cheap too.