Yeah. Least expensive entry now is the Echo Dot. There's a custom command option at the bottom of the list in the Alexa routines.
On HE, you use this custom driver code and create a virtual switch that also has the motion sensor capability.
In the Alexa routine you specify that when that device (which in that part of the routine will how up as a motion sensor or contact sensor) detects motion, then do the custom command. The custom action is whatever you would normally say. For simple ON/OFF, that's probably supported via their skill, so you won't need a custom command for that.
