Good solution for trigger photography?

I remember years ago I was looking for sensors I could use with my camera to trigger when there was sound or passing through a point, etc. At the time there were virtually no solutions and those that did were like $500.

Are there recommended solutions that exist today that are more affordable?

The more sensors, the better, I guess! Or modular

Magic Lantern has that ability. It also has options for triggering the shutter when something enters a pre-focused area. Other options also. Not too bad for a freebee.

Can you drive a soldering iron ? Camera Axe is open source and you can build your own controller and sensors.