Multistrand 12 1/2 ga high tensile will keep them in and is relatively inexpensive. The charger will be pricey, but if you get a good one you'll be amazed at how many other fence projects it can be used for. Remember the elctric fence is only as good as the gound system. Don;t buy cheap insulators. Goodones don;t cost that much more and will last a life time, cheap ones will make trying to find problems seem like a lifetime.
dun