I agree - Macro extension tubes would allow you to use your existing lenses as macro. Be aware though that cheap tubes do not have contacts to allow camera to communicate with the lens. Some expensive ones, such as Kenko Auto Extention Tubes, do ([link]) and allow full auto-focus with the tubes attached. It may or may not be important in this case. I think that for $200 USD the tubes are too expensive, but a used copy may be good to get. I'm looking for one myself.
I'm doing what FSGPhotography suggests. I found [link] on amazon and I'm waiting for them in the mail. I'll be throwing my 50mm F1.8 on the end of that. If I understand things correctly, I'll have about 9inches of working distance and have magnification up to 1.25x.
But, for $22 plus the cost of the lens, it's hard to go wrong. It's probably not as good as using a proper macro, but it's a lot cheaper.
Starting in probably a week I'm likely to start using those extension tubes. Like I said, for the cost it's hard to pass that up, even if you don't have automatic control over anything. Ideally I would have a completely manual lens where I could adjust the aperture manually.
I suggest you take a look at Sigma's 50mm macro lens: [link] (or for lower prices check here: [link] but I don't know the cheaper stores on that list so no guarantees)
I had it for quite some years and really enjoyed it. It's quality is really good it does offer a true 1:1 macro. Extension tubes might be an even cheaper solution but if you are serious about macro I would suggest going with a real macro lens from the start.