Thank you Fergs for your intelegent answer. I actually asked this question on an other forum, and I have gotten two other responces that is worth looking into, with one looking very promising. This is the post.
The first one is this:
"How about using an IR thermometer mounted on a servo? You can always use a range finder to determine the distance to the object. One of those thermometers can be easily obtained for less than $5. You would just need to hack it to make it work in your project. 1k times cheaper though.
Just a thought."
That sounds like a great idea, but the second sounds even more promising, though I do not completely understand what he means.
"Scan a pyroelectric sensor (as found in a PID sensor) with a grating/Fresnel lens back and forth (or better, rotate it) - that way it cannot be fooled by a person standing still.
It will detect even minute temperature changes crossing it and may have to be desensitized a bit."
When doing research on a PID sensor, it appears I can get one for $10, plus they are made exactly for tracking humans in range!
This page says "PIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range."
My only question is, does this know where the target is, or only if it is in or out of the sensor's range?
I hope it gives a whole image to base it off of. I will be programming something to run the whole turret on an old Android phone so I can have the entire thing self-contained. I will use an Arduino setup to run the stepper motors from the phone app's control. I will also have a BlueTooth connection from an other phone with an app I write to use as a remote control for more complex functions like making the turret dance and turn off and stop shooting or mute.
Thanks for your ideas!