One of the recommended products that came up recently for me on Amazon was a set of 2 Makerfocus ESP8266 NodeMCU boards for $15.99. I’m familiar with the chip from using the Adafruit Feather HUZZAH with ESP8266 WiFi that came with AdaBox003. That board runs for $16.95 though.
The reviews for these were good and any issues people had were resolved quickly by the seller. I figured it was worth the little bit of risk to try out these boards as a way to have some WiFi capabilities on hand. When they arrived, I ran a few quick tests in the Arduino IDE and had no problems uploading code or connecting to Adafruit IO with some of the example programs. The boards are slightly wider than the Feathers I’m used to working with, so there is just a single row of holes on either side when plugged into a breadboard. One other difference is no JST connector for a Lithium Ion battery.
If you’re looking for a cheap intro to Arduino or a way to get an electronics project on your network, check out these microcontrollers.