I am looking at getting a macro lens for my D7100. I know Nikon has a 40mm that is very inexpensive, a couple versions of a 60mm, and of course the 105mm VR. I don't know if I want to get the 105 as it is at the high end of my budget. Does anyone have any recommendations for a macro lens? I am shooting DX right now but may go to full frame at some point, so something that would do full frame would be good. I am open to Sigma or other brands as well. Thanks in advance for your input.