Little late here, but for future reference, Mitsubishi sells replacement lamps on their website for $99 for anyone not aware of it. Ex. for a WD65737-915B403001LAMP (180W) (V39/V39+/++/V41/41C/+) 'G' $99
You have to go to support and put in a model. It appears if you put in a current model, they do not list the lamps as an available part, you have to request it through warranty (must be covered 1 year I assume?).
I've had pretty good luck with my Samsung 56" that I bought in 2006. I bought an extended service warranty. A few months before it expired (2010) the tv had turned itself off a couple of times, so I called it in and they replaced a few parts. I was still on the original bulb, but since the plan covered 1 bulb, the guy was nice enough to put a new one in. As a bonus he left the original one since it still worked.