If you are interested in abstract macro photography, you could consider a bellows to increase the distance between your lenses and your camera. With this, all your lenses will become macro lenses. You will have to use a tripod, and spend some time focusing, and work manually with the camera, but the result can be really nice (check my images for a few examples). A bellows should not cost more than 100 €, but is a lot of fun to those that like to experiment and spend time for each shot.