The ESP32 by Espressif Systems

• Cost: around $20 US
• Connection: USB, Wifi, Bluetooth
• Inputs / Outputs: 20 analog inputs, 45 digital inputs/outputs
• ADC Resolution: 12 bit
• Power: from USB or external 9 – 12 V supply
• User must buy and design own sensor circuits
• Programmed from a host computer via USB, Python or C++, including Arduino IDE