It turns out I have a board with the same CPU, but when I bought it a couple of years ago it was $8 against $3 for a pro mini. Now on Ebay at least one blue pill clone is less the $3 (and less than a pro mini). I ordered some to play with.
Another good reference (assuming you can buy more than one at a time anyway). I have a couple of PI zeros, but the frustrating part is that even now you can only buy the $5 version one at a time (which means shipping raises the price unless you have other things you want from the same source) which reduces their usefulness. Thanks for the references!
Peter