where do i go if i want someone to build an electronic device?

Answer 1

It depends on what you want to build.
Does it need to be designed or engineered as well?
If it is simple, the vocational schools have an electronics department where you might find a "star pupil" of sorts who could easily follow a diagram, and maybe even make some improvements for you. If you want to produce a professional prototype of a more complex device then you'll want to look up some companies
see sources for a few examples.

Answer 2

Not enough info. Like the previous answer depends on what you want built. It will cost quite a bit for a professional prototype job. I have more than twenty years electronic assembly experience and can tell you that a prototype I built a few years back cost the customer $5000 for an item that would eventually be sold at $75 each when in production