I have power in a nearby outbuilding.
I've used Ethernet over Power devices with varying degrees of success.
Great sometimes; useless other times.
Alternatively a cheap router/WAP that can be configured as a client at the remote end.
Curious about the camera's Dollar value in relation to the overall equation;
If it's a fairly decent camera, I'd be looking for a solution to keep it in service.
I've got a few Wifi cameras operating here & largely unimpressed & gradually migrating them all to POE cameras;
Just too much Wireless congestion here to get 100% satisfaction.
When you say the existing cable has failed, is completely severed, of just not providing the full 4 pairs.
If it's just one failed pair, you may be able to substitute another for the failed pair.
Phil.