Cylinder ID sensor?

I have been told that in 94, the Ranger/Explorer/Mazda 4L engine used a cylinder ID sensor (aka Cam Sensor?) that is unique to that year. If the sensor fails, a new one is over $500 from the dealer. That is a lot to spend just to find out if the sensor really is bad, especially on a vehicle with over 200K miles. So, does anyone know of a cheaper alternative? That could include a used sensor (I have called dozens of salvage yards only to meet with silence - nobody knows what this is), an aftermarket sensor (maybe?), or swapping the entire engine out. But, 94's seem to be rare so is it possible to use an engine of a different year? Also, I have a 5sp manual - will the trans mate to an engine from a automatic model?