[fencepost]

To consolidate and clarify a few comments:

You can get a non-fixed portable generator modified to run on propane or natural gas fairly inexpensively (the "gas adapter" mentioned above). That can be hooked to either a large fixed propane tank or be used with the smaller tanks often used with gas grills (or be permanently connected to natural gas, but then just get a fixed install generator). Advantages of propane are that it's stable (gasoline and diesel degrade), readily available, you can simply be well-prepared for a heavy grilling season if you don't need to use the generator, and because it's stable and stored you can be somewhat insulated from price swings.

There are calculators available to determine appropriate sizes and approximate runtime based on generator size, load, etc. but a simple rule that I saw was that a 3000 watt generator would likely run for 45 minutes to an hour on a 20-25 pound tank depending on load and inverter setup.