This all started when I ordered five of these little boards back in 8-17-2016 from a seller on Aliexpress. They took a month to arrive (not unusual when ordering direct from China). They cost me $2.01 each, with free shipping. Amazingly they even threw in the strip of 40 header pins to allow you to solder it up and put it on a breadboard. If you are in a hurry, you may be able to get them from domestic sellers on Ebay for a few dollars more. But, what's the rush?
Lots of sellers offer these, and I have seen them for as little as $1.76 each with free shipping. I typically order them in a lot of 10, figuring that something like this is worth having on hand.
Tom's Computer Info / tom@mmto.org