All you need is electrical power for that camera, it has wi-fi already. I don't know if consumer wireless routers will go 300 feet, I doubt it. You might need something like a "Hi-Gain corner antenna" like I have and don't know what to do with (my wife's cousin gave it to me). It says it will boost your router's signal strength from a standard 2 db to 15 db, claiming "up to" 400% range extension.
I assume that this would also pick up the weaker signal from your wireless camera. If the corner antenna boosts the signal going out, it should also be able to boost the signal coming in, or be able to pick up weak signals. Because I can assure you that your camera's wireless signal will not normally traverse 300 feet through a layer of trees.
Here's the one I have:http://www.amazon.com/Hawking-HiGain-Directional-Corner-Antenna/dp/B0000DIET2
The 2.4 GHz band provides much better range (distance) than the 5 GHz band, so you'll want to stick with that. I checked with two wireless router reviews, from Maximum PC and PC Magazine, and both stopped testing at 85 feet, and the throughput was not very high at that distance. So I feel pretty safe in saying that without some extra technology you are not going to get your camera feed from 300 feet away through a line of trees, not at a speed that will allow you to stream video.