Gridlock cameras can be added to red light cameras, also reducing congestion policing costs.
Speed cameras trap people new to an area.
Or they could just, not speed? And speed cameras can be everywhere. They cost up to $50k to deploy and collect to 2k+ fines per year (based in my location, this obviously varies wildly), so they run net positive. Rotating locations can also get after the habits of locals, though that's the 50k cost, I'd guess statics are cheaper.
If immediate reduction is most important than habit changing over time (i.e. a school zone or highway transition) speed linked red lights can achieve the effect. Such to say, if you drive over the limit, the light turns red. This forces you to stop and pisses off everyone behind you, providing social pressure. These are only in the pilot stage, so I don't know the real deployment costs.