The 60mm 2.8 between those options...
What would a refurbished 60 cost? Try Cameta.
If I'm allowed to give you advice Mike, it would be to wait, save up a little more and get a 105 macro. The shorter lenses are good and sharp, but, and it is a huge BUT, if you want to fill the frame with your subject, you'll have to get so close that the lens itself will be cutting your light. And/or you will scare the little bugs away. I bought the Sigma 105 and I don't think I would even think of trying macro shots with a shorter lens.
So, if if was me, I'd wait until you find the right lens, and to me, anything below 90mm is just too short.
I am in that same frame of mind myself but I was asking about the 60mm due to DX crop factor. But, I guess that doesn't change the focus distance of the lens itself and it would still be short.
Thats the one I use and if you know how to light your subject and manual focus then you get some great shots.I have seen the older Tamron 90 macro going pretty cheap (2nd hand) By all reports it is a great lens. Also have a look for a 2nd hand Tokina 100 macro.
You know the Raynox DCR-250 close up filter will allow your other lenses to focus closer.I might need to be a little more clear on my wishes here. I thought about what I want and it really isn't macro. I want to be able to focus pretty close and fill the finder with the image and not necesarily be 1:1 or greater.
I looked at a lens I think I want to buy instead. Nikon AF-Nikkor 28-105mm "D" lens with macro setting. Supposedly very sharp and close focusing.
Why not go reversing ring with your 50mm?