Do the work yourself. Not hard. are you sure you want it above the fireplace? I considered that myself and opted for another wall. the viewing angle is just to weird for me.

Involves mostly cutting and fishing wires. You can run wires behind wall, under trim or in the ceiling, depending on placement.

But I would say average price would be between 200-300 dollars if you have all brackets yourself.

Here, go to AVS | Home Theater Discussions And Reviews. Good installation tips and guides. Just use search.