I have a few SLRs but no real macro lens, and would like to try some basic macro B&W work.
What could be a minimal, inexpensive (extension tubes?) setup that could get me there?
Light metering issues: onboard metering may be weak or non-functioning. Estimate and bracket exposure?
How much "macro" do you want? Is it just to get a little closer for some close up shot, meaning that the subject is a few inches wide? Is it to get into the "true" macro range, meaning that the subject is plus or minus about an inch wide? Is it to get true magnification, i.e. the subject is a fraction of an inch wide?
The most versatile way of getting there is to get a set of extension tubes. You can usually find generic extension tube on ebay for not much money. The problem here is that they are very fiddly to use. For example, if you don't have through-the-lens metering you are going to have to do a lot of calculating for exposure compensation and adjusting your camera settings accordingly. Plus there's the issue of putting the tubes on and taking them off in combinations that give you the magnification you are looking for. Please note that you may suffer a small amount of image quality degradation using extension tubes. The reason is that "normal" lenses are optimized for conditions where the object is relatively far from the lens, i.e. not with the object close to the lens. This is called "conjugate ratio", and lens aberrations depend on the conjugate ratio.
If you are only looking to get more into the close-up range without necessarily getting into the true macro range then a set of diopters might be your ticket. They are easy to put on and take off, and they don't require exposure compensation. The down side is that simple diopters may result in some resolution degradation. However, if you use moderate power diopters and don't stack them, and if you stop the lens down, the images will probably be better than you might expect if you believe all of the negative comments that are often made about negative diopter lenses. Plus, most of the image degradation will occur near the edges of the frame where it usually doesn't matter much. Anyway, who cares if you will need to stop the lens down? If you are photographic three dimensional objects (e.g. not doing document photographs) you are going to do some fairly extreme stopping down of the lens in order to get depth of field anyway. Simple diopters are very inexpensive on ebay, especially if you buy generic ones.
As far as image quality is concerned, it is actually quite hard to find A/B comparisons of images made with diopters vs. other methods, especially if you are looking for shots made under relevant conditions, meaning with the lens stopped down to a significant degree. I did find one comparison in a book where they compared a +6 diopter (which is getting into a fairly hefty diopter range) with a true macro lens, and sure enough there was a difference in image quality, but surprisingly less difference than I would have expected. Reference: p. 46 of the book "The Manual of Close-Up Photography" by Lester Lefkowitz. I am attaching a copy of the relevant part of that page. Note: This is looking at an enlarged part of the corner of the frame, which is where the diopter solution will perform the worst in comparison to a true macro lens, but to me the result looks not too bad. In fact, to me the photo shot at f/11 with the +6 diopter (upper right) is slightly better than the macro at f/4 (lower left) and almost as good as the macro at f/11 (lower right).
If you can get an achromatic diopter (two-element diopter) then your image quality is probably not going to suffer to any noticeable amount. The main problems with these is that they tend to be expensive and/or hard to find.
If you want to get into the extreme closeup range then you should get a 4x microscope objective, an inexpensive set of extension tubes, and and adapter to attach the microscope objective to the extension tubes. This doesn't have to cost very much, and the results will amaze you and your friends. Read about it here:
https://www.closeuphotography.com/seventeen-dollar-plan-4x-objective.
Here are a couple of more links worth looking at:
https://coinimaging.com/add-on_macro.html
https://www.bhphotovideo.com/explor...-solutions/macro-on-a-budget-close-up-filters
One of these links shows what can happen if you reverse a diopter lens in front of a regular lens. The improvement in image quality can be dramatic. This is actually an idea I have been meaning to try for a long time but never got around to it. It's nice to see someone show that it works. However, I would have preferred it if I were the first to show that it works. Anyway, the reason I considered this is that under certain conditions a simple meniscus lens can exhibit zero spherical aberration and zero coma, (the two worst aberrations), and reversing a simple diopter lens can approximately mimic those conditions. (Oops, correction, when I read it again it seems that the article showed what happens when reverse-mounting an achromatic diopter, not a simple meniscus diopter. I am surprised at this result because reverse-mounting an achromatic diopter should not help. Possibly I am reading the article wrong.)
Here's another link worth reading.
https://www.davidkennardphotography.com/blog/865-sonia-close-up-kit-review.xhtml