Use Ebay. I bought a cheap 10 dollar one on ebay, shipped from China. It got here with the light burned out, so I had them ship me a new one. The one without a light, still works, but now I have a new one.
I went to Radioshack and got one there for $22 after price of AAA batteries (Ebay one uses AA). The Radio Shack has a nicer look to it, but it works like crap (It's the same one in that link up there). It's from china too, but twice the price while the eye piece is half the size. Even at only 30x zoom, you can only see a field of 5 trichs or so.