What would be a good Macro lens for the Nikon d3100, at a reasonable price?

What would be a good Macro lens for the Nikon d3100, at a reasonable price?

The best would be the Nikkor AF-S 60 mm f/2.8.

The most reasonable price would be a good used Nikkor AF 55 mm f/2.8 or AF 60 mm f/2.8. As with all non-AF-S lenses, you will need to manually focus your subjects, which actually is how you shoot macro subjects in any case

Depends on what you mean by reasonable. The AFS Nikkor 85mm f/3.5 micro is the least expensive lens macro lens that will autofocus on your camera. The Sigma 50mm f/2.8 macro is the least expensive worthwhile choice to go for if you don't mind focusing manually.

Alternatively, be on the lookout for used macro lenses such as the older AF Nikkor 60mm f/2.8, Sigma 105mm f/2.8, Tokina 100mm f/2.8, Tamron 90mm f/2.8, etc.

The best deal in terms of cost would be the Sigma 50mm f2.8 macro. It's a pretty good lens but you'll need to manually focus it on your D3100.

Here's a shot I took with it on a D300;