There is a lot more in a PSAP than a typical call center. First of all, they are also paying a portion of the networking costs that get the calls to the call center. Then the skill level for a telecommunicator is a lot higher than a call center, and the manpower costs are probably twice or three times your number. Then they also have to overstaff it - you don't get a "we are experiencing a large volume of calls..." from 9-1-1. They have telecommunitors waiting for calls, not callers waiting for telecommunicators. Then they have dispatch systems, which have accompanying record management systems.
And all of it has to be reliable, and it's specialized for 9-1-1, which is a limited market, and the net result is that the systems are expensive. If there is not a lot of diversion, the surcharge pay about half of the cost of running the system (not including responders).
If you doubt it, DOT paid for a study a few years ago. Booz Allen did it. I'm sure you can find it if you want to look. Total cost of the system at that time was $2.3B. Has lots of detail on where the money comes from and where it goes.