You will need a generator rated for 700 watts continuous. I went with a Ryobi 900 watt propane generator and am happy with it. The 900 is peak which is only about a second or two. It is 700 watts continuous.
What area are you in? Craigslist often has good deals. I would look for a 1,000 watt Honda or Yamaha. Champion makes good generators as well. Get the inverter type as they use less fuel and are quieter.