What is the reward for defeating all 17 Cyberpsychos?

There is no in game reward beyond the eddies you make while completing these missions for Regina. There is also no follow up mission once you have completed all of them like there are with some of the missions in game. You will get between 1000 and 3000 eddies per mission you complete.

Once all of the cyber psycho sighting missions have been completed you will earn the achievement "I am the law".

You got handed some Eddies. It’s easy to miss when that happens.

As with most missions, the cash is the only direct reward.