Extension tubes, like Kenko, usually come in a set of 12mm, 20mm and 36mm giving you 68mm if you stack them all together. 68mm will give you around 1.5X magnification. Add a 1.4 Teleconverter and you can get to around 3X. You will need a flash or other light source as tubes and TCs cut down the light reaching the sensor.
Make sure the tubes you get support aperture control and AF.
Or just save up for the ultimate macro lens, the Canon MP-E 65mm