I've been walking on nature trails a few times a week with my parents, and really wanted to take a few macro photos along the way. I don't have a real macro lens and didn't feel like mounting my only normal camera lens backwards, so I thought I'd try a primefilm scanner lens I had lying around which I'd never figured out how to mount. Now that I have a 3d printer that was pretty easy:

I tried it on bellows at first but the mag was too high for handheld use with ambient light. I tried mounting it flat like this (since it's only 45mm from the sensor when in the scanner) and it covers aps-c just fine at about 0.3x (75mm FoV). Seems to be adequate for casual walking around on an extreme budget.
Red Chanterelles(?) by
Stephen Challener, on Flickr