Extension tubes for nikon d5100?

So, i have a kit lens i.e 18-55mm and a 70-300 (VR) telephoto zoom lens. For macro photography i heard kenko extension tubes are the best. Are they?
and gives the same image quality as we get from a good macro lens. I want really close and sharp pictures of insects. And their eyes, like we see in actual macro photography.
I live in India, so please suggest me good extension tubes within a range of rs.10, 000 (200$) .

If you are going to go with extension tubes, the Kenkos are the way to go - but make sure they are the type with the electrical contacts in them so that you can adjust your aperture. You don't need a lens with an aperture ring if you buy the better tubes - only if you buy the cheap ones (as they don't have the electrical contacts to set the lens aperture).

Don't worry so much about autofocus as most macro shooters use manual focus anyway (autofocus is not that good at close ranges).

Extension tubes are the best low-cost solution, but still not as good as a bona-fide macro lens, as you are still using your kit lens. It would be better if you could spring a few dollars for a 50mm prime as well, but then you are looking at the cost of a macro lens (such as the Tokina 100mm macro).

But it is a good way to see if you like macro. However, you will quickly learn extension tubes take awhile to setup (as opposed to a macro lens), so they can be frustrating (and there's enough going on with macro anyway).

The one thing you will not be able to match with extension tubes is lens sharpness, as macro lenses (true prime 1:1 macro lenses) tend to be the sharpest lenses made. And being prime lenses, there's usually no distortion in them.

Still, they are expensive, and you can probably start out with extension tubes to begin with.

One issue though. You will quickly find that you may need a tripod, remote shutter release, and close up flash. Close up flashes are among the most expensive you can buy, and if you go with the Nikon flash, it will cost more than your camera.

Macro is perhaps one of the most expensive disciplines in photography. But it is probably one of the more technically challenging aspects of photography, and is is very rewarding when you get those awesome photos.

So yea, buy a good set of kenko tubes and try macro photography.

I'm not sure if they would be a good idea in combination with the lenses that you currently have.

While the description says that the lenses retain autofocus and metering capability, i'm not sure if the latter applies to AF-S lenses. Based on what i read there i have feeling that it only applies to the older screw-driven AF, not AF-S.

Edit: Based on http://www.thkphoto.com/products/kenko/slrc-04.html AF-S autofocus will work
/Edit

Also, on the photos i don't see an aperture lever or anything like that, so you will likely lose the aperture control if you use them with lenses that don't have an aperture ring. That will render them nearly useless for macro purposes due to the extremely shallow depth of field at wide open aperture.

If you really want to do macro with a budget of $200 or less, consider getting the older 50mm/1, 8D and a set of $10 extension tubes. You'll lose metering as well, but with that lens you can set the aperture manually using its aperture ring. The exposure can be adjusted by trial and error then. I use this method myself.

Of course, that older lens will not autofocus at all on your camera, neither with nor without extension tubes. If you ever upgrade to a D90 or D7000 or their successor, then that lens will autofocus on that camera.

Edit2: AWBoater, are you sure that the aperture in Nikon lenses can be adjusted electronically? So far i thought that this would always happen with the mechanical lever.
This thread also seems to imply that it can work electronically