Hi, I always had electric fencing for my horses. Go to Americanlivestock.com that's where I've bought it all. You need the "shock machine", which is your biggest expense. Then you need 3-8foot grounding poles to beat into the ground at 8 feet apart. You need a piece of thick wire to fasten to each pole and then to the zapper. You need shock wire, I think aluminum throws a good shock, polytape, a fair shock. And these little yellow insulators that you nail into wood, and they hold the wire away from everything. Just remember, this does stop horses and cows. I would do several rows of wire-the more the better. This wire also stopped the herd of hungry deer that ravaged my garden.
So the zapper is probably around 50-125 bucks, the poles are I think about 15 bucks apiece, the piece of thick wire, cheap, the shock wire, cheap, the yellow wire holder insulators, cheap.
Of course, the pulley on the tree sounds good, but it has to be hanging way out, bears do climb. Karen