I have successfully installed a number of video surveillance cameras up to 1200 feet from the monitor/power supply using CAT-5 twisted-pair wire.
Several suppliers offer small adapter units to place at each end of the CAT-5 cable to feed DC to the camera and receive video back to the monitor. Check out www.supercuircits.com
. The main problem with CAT-5 is that its' DC resistance is approximately 30 ohms/1000 feet. This means that there is 30 ohms in the DC feed wire going TO the camera and 30 ohms in the DC return.
It is possible to modify the adaptor modules so that spare pairs of wire are paralleled in order to cut the resistance in half.
I solved the problem of excessive voltage drop by using a power supply with a higher voltage output and installing a simple little 3-terminal regulator at the camera to drop any excessive voltage back down to the required 12VDC. Whatever you do, calculate the voltage drop based on the total resistance in your CAT-5 run and use a power supply that puts out 5 to 8 volts above that and let the 3-terminal regulator drop the voltage at the camera site back down to the required level.
The video coming back from a 1200 foot run of CAT-5 cable is just a tad soft from high-frequency roll-off, but is still at least as sharp as a the video playback from a typical VHS video tape cassette player.