PCB Design and Fabrication
When you have a circuit that you need mass produced you will generally want it to adhere to standards. This goes a long way to ensuring your prototyped circuit will work all day, everyday, in the real world. In addition to reliability and compliance, a proper PCB design can lead to smaller and/or more efficient circuits.
When it comes time to actually product the circuit boards, you need a fabrication house you can count on. The types of fab house available these days really run the gamut. Some will spit out your design completely as is, whether it works or not. Others have entire departments dedicated to circuit validation and testing, and truly everywhere in between. Prices will vary accordingly.