Starhemie clear bumper case and Lightning Knight Ultra Slim Scratch-proof case they are both 8 dollars and if you want tk know about more cheap and beautiful cases ~~https://www.gottabemobile.com/best-oneplus-5-cases/?gbmsl=1. AND YEAH karbonn bumper is also great too
To be honest with you and perhaps some people will disagree with me, the best case I've found so far that offers great protection but without the HUGE bulk is the otterbox.
I know usually you hear or read otterbox and right away think huge bulky case. This case isn't like that, but still offers lots of protection.
I've spent lots (way too much $$ in fact) on cases since I've had my OnePlus 1, OnePlus 3 and now OnePlus 5 and to be honest, all the "cheap" cases have either offered no protection or they feel cheap and break/crack easy when dropped.
Only reason I bought the Tudia was because it has the ports plugs builtin for both USB and Headphone to protect from Dirt and built in screen protector.