Why is half of my screen dead?

i have a basic mid 2009 macbook, which i use quite frequently. about six months ago, the bottom half of the screen would start flickering and changing color, sometimes displaying an upside down depiction of whatever the screen was showing. for a while, if i tapped the back of the display in the right place, usually near the apple logo, these problems would disappear and the screen would work fine. for the past few months, though, the damage has been permanent.. exactly half of the screen (bottom half) is a washed out white or black with a few vertical strips of other colors, and sometimes fades from white to green, also. the top half works perfectly, and the computer functions just fine when plugged into my monitor.

the folks at the genius bar say they tested the cables etc., and believe it to be a logic board problem, but i was wondering if it could simply be a large amount of dead pixels that could be fixed with an LCD replacement, as i have a few spare compatible lcd's around, whilst the genius bar recommendation of a flat rate repair was in the hundreds.. thanks very much in advance!