Homebrew PCBs

You need to contact some of the PCB assembly companies to get the 
exact details and, of course, prices.

I have purchased bare boards in small quantities (up to 50 in one 
order). There are many companies that will do this. And many of them 
will assemble the boards for you.

One of my favorites is Advanced Circuits. They will do one or three 
boards for prototype work or any number for production.

http://www.4pcb.com/

They also do assembly, either with parts that you supply or they will 
supply them or a combination of both.

http://www.onestopassembly.com/

I have not used their assembly services so do contact them AND OTHERS 
for the details.

One thing that I would think would be absolutely required is that you 
should be absolutely sure of the design and the fit of the parts 
before placing an order. Do one or more prototype boards first and be 
sure to use the actual parts that will be used in the final assembly. 
Fiberglass does not stretch worth a darn.

If you are using some of the smaller pitch devices, like BGAs, you 
may want to have them assemble the prototypes too. It will cost a bit 
per board, but you can be assured of a proper assembly. Add the cost 
of those prototypes to the first run of production boards when 
figuring the sale price.