Not arguing with you, marginal cost is indeed near to zilch. However if unit A is legally required to have the service and unit B is not you have to have some system that allows unit B to get it at very low cost if you want to encourage them to provide it. It's human nature that Unit A will then argue for Unit B to pay a "Fairer" proportion of the cost. Problem is also that while the marginal cost of providing the data is zilch, the cost of delivering it is not. If you want a point to point secure circuit with assured bandwidth and latency you have to pay for it. I think we recently got a 2 Mb/Sec point to point put in around 10-12 miles radial distance and the rental is around 7.5k p.a.
There is of course also the issue of how much of a service you can provide. Any radar service is very manpower intensive. No doubt one of the controller chappies can advise us of how many contacts can reasonably be handled per controller.
I wasn't just thinking about Stingers, "OK lad's the police chopper's on it's way, drive away carefully and look natural" springs to mind. Establishing a pattern of operation could also be useful.