Mass produce it for $50 your cost, or would retail for $50?

In my opinion, the thing you have to be very mindful of, if a product like this gains wide acceptance, expect competition from the already established accessory producers. Patents rarely protect you over the long term, so producing the product at a low enough cost so that your competitors don't see large enough retruns to jump into the market is key.

Another approach would be to contact accessory manufacturers with your idea (have non-disclosure agreements ready) and work out a licensing agreement. They produce it, market it, distribute it, you get a royalty check.