Robert, I would recommend an Xrite, Macbeth, or Tobias, (there are others, but I don't remember the names) but I don't know exactly what you are using it for. I guess that it is for BW calibration. If so, you can do this with a single channel transmission type. If you use Pyro film developers, then it would be better to have a digital model so that you can still zero with the blue filter in place. I bought an Xrite 301 for less than $30, but it was sold as 'not working, as is'. I took a chance. It turned out to need a fuse, an aperture, and a bath -- so I lucked out.
I'd stay away from old Kodaks or Westons. They work, but not as well. Wait for a digital unit that won't be perfect but okay for your use.