I guess it depends on how much fencing you need to install. Will you have other uses for a new air tool? Do you have the compressor already? Look at pawn shops and craigslist as well.
HF tools are hit and miss, and often don't have the same nail options as professional tools. A siding nailer that uses coil nails would be a better option for rental fro just this job. Personally I would use screws instead of nails, so that any damaged boards could be replace easily in the future.
It depends on how nice of a fence you're building. For cedar, stainless nails or screws are the right fastener, as galvanized will stain and streak the cedar. Again it depends on how you want it to look, if you're painting then galvanized will work. Personally I like the weathered and streaked cedar look of unstained cedar, and also use a wood treatment called Lifetime or Eco Wood Treatment to get the old cedar look on purpose.