You can answer questions like this by going to one of the major online camera sites, B&H Photo or Adorama and using the lens-browsing tools they provide. Here's a search that gives you a list of current offerings:
Basically, you've got a ~ $300 option, a $450 option, and a $600 option, all of different focal lengths. The cheapest one offers 1:2 magnification and the others 1:1. The more expensive models are also nicer in other ways — for example, the 60mm has a circular aperture, for nice bokeh stopped-down.
All three autofocus, but for real macro work, you probably want to focus manually very carefully anyway.
These are not 2:1 lenses, but you can get good results even with 1:2, and even without a macro converter — I've not used one of those, but reports I've seen show that you can often get better results just cropping extravagantly.
But there's another possibility which may be even better and quite likely cheaper — extension tubes.
You could also expand the search to third-party macro lenses, several of which are excellent, especially for the price.