Anyhow, I came up on this plastic cup. It appears durable with little flexing. I figure a 1/4" drill bit could make some quick drainage holes. I opted for the gray as it is the brightest, non-red color that they had. It's specs are:
3-5/16" top diameter
2-5/8" bottom diameter
Cost: $0.55 w/local tax included (not as cheap as the 20oz foam cups from Chic-Fil-A, though)
Kind of narrow, though. But, the bottom "corner" is pretty square so the cup seems to be rather stable. It might work for a low-growing flytrap that wants to hang over the edge of it's pot (or even an upright-growing one, I guess) or maybe a couple of sundews. I've used it a good bit so far...dipping water out of buckets.<grin>
Just thought I'd pass this on in case someone's looking for a narrow but tall pot. FWIW.