Here are a few tips that might help. First, you need to get a completed prototype built of you product. Then, you should get it patented. After you get your devise patented you can start looking at contacting manufactures. They can tell you how much it will cost to mass-produce your devise. Also, keep in mind that manufactures have their own list of suppliers. You don’t have to worry about that aspect of production.
You should get a prototype built and start working on securing a patent. But I would look for a manufacturer as you are looking to get your prototypes built. In my experience with PCB manufacturing the manufacturer will also produce one or two prototypes for you, after which you can make needed adjustments if necessary. The benefit of selecting your potential manufacturer to produce your prototypes is that you are able to get a feel for the manufacturer, develop a relationship with them, and decide before mass production if their quality, service, and pricing are what you want, while getting your prototype made as well. Kill two birds with one stone.