Id second the itp A1 EOS. It is about 24 bucks, minus 10% discount from goinggear, so its in range.
It can use a CR123, RCR123 or 16340. It is a twisty which I like because it won't come on in your pocket.
Its the smallest CR123 light that I know of, 2.3 inches long, 0.8 inch diameter. It has 3 modes, a 2, 30, 200 lumen. Good flood, nice beam, and definitely wearable on your keychain (though it does come with a removable clip).
I love mine. Nice white light.