In absolute order of importance!!! (unlike some of my posts that are not in order of importance...)
NUMBER ONE!!!!! Forget your idea as stated. Completely put it out of your head. NOW! Power junction boxes should NEVER NEVER NEVER be mixed with telecom. It is a violation of the National Electric Code and your homeowner's insurance agent will thumb his/her nose at you when your house burns down. Separate boxes. Period.
2) If you are looking for reasonably priced wall plates and connectors, interestingly enough, your local Home Despot or Lowes has a pretty good selection in the electrical department.
I am looking for a good place online to purchase rj-45 wall receptors. I need one that has a power outlet on top (or bottom) and an rj-45 outlet. I am looking for a place that deals with volume and has a low price. If anyone has found such a place, please let me know.