My problem is I *just* want the mouse tray. Most trays I saw are keyboard + mouse. I prefer my keyboard on my lap. (My keyboard is a Kinesis and about 2" deep, which makes the ergonomics just right.)
I did find a couple mouse-only trays, like this one: http://computers.pricegrabber.com/input-device-accessories/m/4292501/, but $100 seems pretty steep. I just want a tray that bolts or clamps to my desk.