I will second the ESP32. It's sub $4 in most places, has a dual core processor, BLE, WiFi, hardware PWM and I2C, and much more. Also their C SDK environment is

I will second the ESP32. It's sub $4 in most places, has a dual core processor, BLE, WiFi, hardware PWM and I2C, and much more. Also their C SDK environment is quite pleasant to work in.