I've got another off-the-wall DIY idea that just might work: I've got an old Beseler 23C enlarger that I really don't plan to use again. I've decided that it might make a nice adjustable macro platform.
First of all, it has sturdy twin girders that you can crank the whole enlarger head up and down with. Then, turning your attention to the enlarger head: It can be pivoted 90 degrees (to project at a wall instead of the baseboard). I'd like to rig something up so it could be tightened to hold any angle between zero and ninety.
Then, imagine your camera affixed to the enlarger lens stage. The lens stage has its own focusing rack (and knobs) which give you a fairly "fine-grained" macro stage movement. This allows you to rack the camera in and out for macro focusing.
Essentially, the enlarger (with little modification) can be a combination low tripod/camera stand & macro stage.
If you are patient, Beseler enlargers like this go pretty cheap on eBay. Even with shipping they would be a lot cheaper than a commercial macro stage alone.