And just to throw this out there: It's not necessary to have a macro lens to take macro photos. What's the difference between the Canon 100mm macro and any other 100mm lens?
1. The Canon lens is designed to give you 1:1 (whatever you are taking the picture of is life-sized on a 35mm sensor) at it's closest focusing distance.
2. The glass inside the lens is really, really sharp. (That's what costs so much.)
Having a macro lens makes it really convenient to get pictures at 1:1. The good glass is also really, really nice. But can you take a normal lens and get 1:1? Yes. You need to move the lens away from the camera a little bit. The easiest and cheapest way to do that is to buy some extension tubes. ALL they are is a hollow piece of aluminum that moves a lens away from the camera sensor. The nice ones (you want the nice ones) have electrical couplings that pass information from the camera body to the lens and vice versa.
The usual rule of thumb is that you need 1mm of extension tube for each mm of your lens: a 100mm lens would need 100mm of extension.
Now, you will lose some light but lack of light is the major problem of macrophotography anyway, so you'll be fighting that issue whatever you do.
Are there other ways to do macro on the cheap? Yep. If you are interested, let me know.