Macro attachment for Tamron 18-200

You can get either a close-up filter or get Kenko's extension tubes. This would be the cheapest route to go until you want to invest in a specific macro lens.

Or for even less money, just hold a large enough magnifier in front of the lens for the occasional shot. You won't get pro quality, but you should get images for practice.

The cheapest method is extension tubes. Yes you will lost some light, but screw on macro filters degrade image quality, whereas tubes will not. If you get the threaded tubes, these are amazingly cheap, but bayonet mount tubes are more expensive

Thanks to both Marcel and Peirro. The Kenko tubes are expensive but what about these?