Cheapest place I've found for diamond wheels, stones, and files.
Bought 10 wheels for $7.00:
Three years ago, I bought these wheels:
A couple files:
I use them a lot and they still cut like new. When I first got them, didn't think they would last this long, not for this price.
I use them to sharpen Forstner, lathe bits, etc. So far, they are going strong. The 600 grit wheel is too fine, unless you want a mirror smooth finish, such as router bits. The 100 grit will really hog off the metal when you need to.
If you get the chance, check one out.