Macro lenses are expensive. There is a cheap alternative, though, that can transform a regular lens into a macro lens: extension tubes. Extension tubes are simply hollow tubes that you put between the lens and the body of the camera. Optically inert, they shorten the focal distance and depth of field and bump up magnification, at the price of a loss of light.
An extension tube can be hacked from any tube of the right size but the more comfortable and still affordable option is commercial tubes with electrical contacts. I bought a new set of tubes for $76 last week, in addition to the one I already owned. Having a good set of various lengths enables me to adapt to a wide variety of situations. The neat thing about having a set is that you can combine them to reach amazingly short focal lengths and magnifications:
To illustrate the effect, I shot the same subject (a Lego minifig) with different lengths of tube and a fixed 50mm lens. Here are the results...
First, here is a shot without an extension tube:
Then, with 13mm of tube:
And finally, all in and diminishing returns with 90mm of tube (13+21+25+31):
In that last shot, the subject is very close to the lens.