It varies and it's very very specific to what you want to develop. The concrete design of your circuit matters. Also prototype building costs are usually a factor 10-100 higher than series. If you already have your prototype then you can shop around various manufacturing companies. To do that, you need Gerber files (your PCB design) and a bill of materials. You also need to think about casing: designing it and creating the mold is expensive. If you don't have your prototype yet, I recommend having it engineered in eastern Europe. Custom engineering is cheap there and high quality. IP protection is a problem. One thing to do is to distribute the work to different manufacturers. For the design phase you are safer if you design your prototype in Europe or the US where international patent laws apply. I could give you more specific advise in a phone call, getting to know a bit better what you are trying to build.