The listing, Fotodiox Canon EOS Macro Extension Tube Set for Extreme Close-Ups has ended.
I got this lens from Amazon for around $15.00. I personally wasn't as impressed by it as I thought I was goingto be.) I used it maybe 3 times.
(Description from the Fotodiox site)
A macro extension tube is a wonderful substitution to expensive macro lenses. It maintains the original optical quality while transforming the lens into a macro lens. It is far more desired then the add-on close-up lenses, which will alter the optical quality. The extension tube will work with all Canon EOS cameras, digital or film.
The camera mount coupling adapter and lens mount coupling adapter can be used independently of the extension tubes or you can add in the tubes for extreme Macro photography. Because no other optical components are added with this kit, the image preserves the original optical properties of the lens. This is an affordable and simple way to turn your existing lens into a MACRO LENS. This tube set includes a lens-coupling ring and a body-coupling ring; three extension tubes of various sizes are also included to build up to the desired magnification.