Another alternative could be the Tamron 90mm f/2.8 Di ?
Here´s what bythom.com has to say about it, at the end of his review of the Nikon 105mm :
"....I've also been using a Tamron 90mm f/2.8 Di, the "classic" moderate macro lens for those on a limited budget. I'll cut to the chase: if you can give up the VR and AF-S and need to save money, the Tamron is the lens to get. I've tried pretty much everything in this range, and though the Tamron isn't a fast focusing lens, it is optically superb....."
So, can you give up VR and AF-S ?
Would be interesting to hear some opinions on how useful VR or OS is in the macro situation.
Here is another quote from bythom:
" ...The closer you focus, the less VR has an impact on the final image. At 1:1 (the closest focus distance), it may not impart any benefit (it didn't seem to in the testing conditions I could create). So do you turn VR off when working in macro? If you're pressed up towards the limits of focus, I'd say yes--you're wasting battery life and potentially making it more difficult to hit a focus point. But if you're focused out beyond two or three feet (~.7m+), it probably makes sense to leave it on, as you'll get some benefit (though not the four stops Nikon claims for the system unless you're focusing far further out into the scene)..."