Regarding having officer cameras streaming back to the police station, and cost of said cameras. The real financial killer here is the support hardware required (cam streams to car, car caches and re-streams to HQ, hardware
like this), and the software back at HQ.
The commercial VMS softwares (and associated server hardware) that handle this scenario (record 10s to 100s of incoming streams and can verify whether a video was tampered with or not (required for chain of evidence)) are generally not cheap. Generally a $X/license kind of deal which can be quite a bit more than the per-camera hardware cost.
As mentioned the cheaper solutions (GoPro, etc.) are generally easily tampered with (gee, I don't know what happened to the SD card!).
All that said, on-body cameras with all the above associated stuff would be money well spent IMO.