I have a working prototype of a small consumer electronics device that I made with Sparkfun breakout boards. I have the schematics and parts list, but I have never done PCB layout before. I could learn how to use Eagle, but I don’t know how to design the board so that parts such as switches and connectors fit would fit snugly through the device’s plastic enclosure. I’m not sure where to start. Is there a good company that would do pcb layout, assembly, and create a plastic enclosure for a relatively cheap price? Like a few thousand dollars? At most, the size of the device would be 2" by 2". I don’t plan to make a high volume of this device to start with, I just want something that is professional. Any advice? Thank you. 
Just start using Google and search for tutorials.
pcb layout, assembly, and create a plastic enclosure for a relatively cheap price?
I can do the PCB layout for you. I am almost done with another client’s board. Once you approve the board, send it off to a fab house and once they return, I can assemble some to make sure they work. After everything works, you can have a fab house do mass assembly for larger runs.
I can also design and model the enclosure for you. I use Solidworks for 3D design and I have a 3D printer to make some prototypes. Once you’re happy, you can send the 3D files to a factory for mass production.
If you want to chat about me designing the PCB and/or the enclosure, send me a PM with your email.
Thank you for the offer! Do you have a company?
So maybe my biggest question is this:
Do PCB layout designers take the mechanical assembly into account when parts like switches need to cleanly fit through plastic? Or is the custom enclosure created after the PCB is done?
I can account for enclosures like placing switches, headers, buttons, mounting holes, etc. But the enclosure has to be designed from some aspects of board design, like height and size of the board.
I do have a website but I am upgrading to utilize HTML5 and CCS3. If you want to email me, I can send you some of the boards I designed. trevor@rossrobotics.com