Looking for an inexpensive Smoke Detection Sensor
I'd go for the cheap smoke alarm.

The actual sensor is a black plastic chamber with a LED and a photo sensor.
It is constructed so that with clean air no light reaches the sensor,
it passes the center of the chamber and is absorbed on another side.
With smoke particles in the air some light is reflected towards the sensor and off goes the alarm.

As for the electronics, I opened up one such alarm and found an MC145010.