To be quite honest, an X10 system likely
will not help you here.
300ft is well outside the wireless transmit
range. Even if you got it set up, the X10
cams are tiny, and provide very grainy
images. The lowlight cams are barely
nightvision cameras... they require a good
amount of light nearby to work, and even
then are really only good for shapes and
motion.
In other words, if you're hoping to catch a
car make and model, license plate, or face,
with a camera, X10 will not do it.
However, if you want to go through the
trouble of getting these systems to work
outside of their inherent limitations so
that you can sit about and monitor live
images for motion or activity, these cams
may work... it would be more trouble than
it's worth, however.
NOTE: X10 cams, in general, work well for
what they're designed to do. The only
reason I may sound disparaging here is it
sounds like they need something outside the
reasonable range of X10 camera systems.