WEMOS released a new development board with ESP32 called LoLin32 with price $4.9 (+ shipping, $2.59 in my case).
WEMOS has released LoLin32 a few weeks ago. Here is link to the news..
The Lite version of board is smaller, it also contains battery input, micro USB connector and reset button.
The most important news is version of ESP32, the ESP32 REV 1. ESP32 REV1 should be fixed a few bugs from REV 0.
The price of ESP32 board LoLin32 Lite is $4.9 (+ shipping, $2.59 in my case).
Wemos wiki https://wiki.wemos.cc/products:lolin32:lolin32_lite