Without a doubt spend $100 to file a quick Provisional Patent, then keep your original R & D with a reputable U.S. case maker until you have perfected it. If your idea is a good one and you give even a hint of it to a foreign maker (especially a Chinese manufacturer) you can instantly kiss it goodbye. If, instead, you keep it in the U.S. until it's patented you can prevent foreign copycats from bringing it into the U.S.
Do some research and check out some inventor's forums. A provisional patent is very easy to write, cheap to file, and gives you a year of domestic protection while you develop it before you move forward to file for a full patent.
TW