We are also building a new home and plan to have the tv over our gas fireplace mantel. Our builder ran the tubing from above the fireplace to the basement and then from the basement up to the study, which is where the components will be kept. I believe we were only charged $50, so yes, $300 sounds excessive. This Tuesday we have Best Buys Geek Squad coming over to look at our setup and recommend a tv size for our space. We plan to have them do the install. One thing that we were told at BB was to have the outlets (power and tube) located toward the top of where the tv will be installed. Of course, ours are located right in the middle of where the bracket would be installed. We'll see how that is dealt with.

In this project (pictured) we used an electric fireplace, which have different clearance issues compared to a wood or gas fireplace. We ran wires up the wall behind the entire unit (the unit we constructed was done in two pieces, so that the fireplace unit below can be removed if ever the electric fireplace needs servicing) For the tv, you need to allow for a plug behind the television (check the specs of your tv bracket/arm to see where the best place is for the plug) as well as the cable (if applicable) For this project, we also installed the cable box directly to the back of the tv, physically attaching it vertically using Velcro, and then ran a satellite eye from the cable box to peek out over the top edge of the television so the remote signal would reach. We also allowed enough clearance around the tv for heat to escape from the tv, and so that you could grab the edges of the tv and pull it away from the wall (on the arm). If you make the surround too close to the size of the tv screen, you could have issues, especially when the tv breaks and you need to replace it, as tv's vary in size. For the depth of the surround, we made sure the tv when affixed to the wall would be within the "box" of the surround, as opposed to making the surround just a couple inches deep and having the tv stick out further than the surround. Hope this helps you!

Here is what it looked like when we bought it--former owner's furniture. I don't like the light colored furniture--trying to decide if I like the large cases next to it. . The rest of the room for now only had a couch and chair.

My TV is above my fireplace, and it's a bad spot. You have to crane your neck or support it to look up. TVs are better placed lower down to the floor.