Seeking,
If you have an attic above you might be able to do this fairly easily as Randy (Sirquack) says. Otherwise you can try the 'behind the baseboards' trick which was previously mentioned and is not too difficult either, although it may have you replacing/repairing baseboards depending on how easily they can be pried off of the wall.
Hint on the baseboards - if your wall is painted you should run a sharp knife (boxcutter, exacto) along the corner of where the baseboard meets the wall to make sure the paint does not stick to the baseboard and peel off the wall as you pry.
No idea on costs to hire someone for this, although I would think any competent local AV shop would have an installation service that could get you a quote.
