A normal intersection the last time I checked was up to $250,000+...depending on the size and complexity of the intersection. I'm sure these lights would be considerably less considering it's essentially only 1 sensor vs. at least 4 not including turn lanes. 
I don't recall sensors be layed at the end of the onramps or in the freeway/expressway/highway lanes so I'm sure they are tied into the Georgia Navigator camera radar system to determine the flow... 
