I would suggest going for some extension tubes rather than getting a new lense, this way you can turn all your lenses into macro lenses. Just make sure if you're using af to get an extension tube with CPU contacts. you're probably gonna lost one or two stops, you would do so with one of those cheap close up filters too, so depending on how fast your lense is this migth be an option.
The other 'dirt cheap' and slightly hazardous option for a dSLR is to take your lense off turn it around and hold it up against your camera body and take your photos like that... it works but remember you're not using film so any dust getting on your ccd will be a problem...
this method is popular with photo students as it costs nothing!
The disadvatange is that you have to set it on manual mode and the aperture ring is on the other side of the lense so you'll be working at the widest aperture...kinda...
hope this helps...
a..//