$12.37 shipped to the US for an ESP8266 with AA battery holder and button style case. Not much feedback though, and the words in the url don't match the product...so it's a bit of a dice roll.
The quality and consistency of firmware/functionality/hidden stuff on the various 8266's I have leads me to avoid them. I had a pair that phoned home to some Chinese domain and registered all via HTTP, and a quick Wireshark yielded it phoned home for commands. Not on my network...
You can pick them up cheaper on ebay, as well.
It depends :-)
Some seem to have a fall-back or fail-safe that isn't overwritten. Even with flashing known firmware, the reliability of the little guys was questionable. Random lockups and very touchy to power source.
https://www.aliexpress.com/item/30-energy-saving-CC2541-ibea...