I have used the several parts below for long distance networking without powering cameras, however the Highwire Powerstar is nice since it shows wattage available at camera end with power led indicator.

The altronix part: eBridge1CRT  is working great at a job for close to 10 years but needs power at both ends :-( .

This altronix part is also nice : [Link: altronix.com] since it only is powered at head end.

Lastly, the Veracity Highwire Powerstar unit works great : [Link: veracityglobal.com]  but very expensive and "Base" and "Camera" side are separate part numbers.

Using coax to ethernet adapters definitely will add big $$$ to proposal.  TVI is pretty nice quality video if you can do a hybrid NVR system using both TVI and IP cams for integration and higher resolution.