Here's a thread on merino wool T-shirts I started a few months back, and like scroca said, there are quite a few more in the Forums:
http://www.bikeforums.net/showthread...-shirts-anyone
Turns out, if you are picky about how the stuff has been made (mulesing, country of manufacture), you have less options and the price will be higher. I ordered two shirts from ChocolateFish mentioned in that thread. After using those for a couple of weeks, I tossed all my old synthetic "technical" shirts in the recycling bin. Their stuff is over your price range, but if you're not particular about production details, you'll find cheaper pure merino alternatives from other manufacturers.
--J