This is some mightly expensive electric - $800+ for a week ($3200 per month)! What do you pay for propane down there - I just filled my tank at somewhere around $1.80 a gallon a couple months back.
Kevin - This is my biggest complaint with the whole house units - they are fuel eating monsters. If money is not a problem I guess they are the way to go. Myself I'm too cheap to burn more fuel than I need to get by.
I have a Honda EU6500is inverter/generator which is extremely fuel efficient. I'm hoping to pick up a Honda EU1000 or 2000 for small power requirements. I still have my old water cooled Honda 6500 in the barn and I use it to power the well (3 hp, down 450 feet) during long term outages. The EU6500 can easily handle the two refrigerators and two freezers, plus some extras for comfort. I have a dual fuel Trane furnace and a 1000 gallon above ground propane tank. I've lived quite comfortably through more than a few power outages, some as long as 3 weeks in the middle of winter - here is SW Missouri.
My fillup a couple of months ago cost about $2.70/gal (and that's in SE Texas). Following Ike, my genset ran for four days powering everything (including A/C) at an average of about one gallon per hour. Even at the higher price I currently pay here (and I paid a lot more for LPG right before Ike), that's under $500 per week. I know...still very expensive. But, the specs for an EU6500isa from Honda's website say that it uses almost one gallon of fuel/gasoline per hour at the rated load. The specs for my 22kW genset show one gallon of LPG per hour at 25% load, which is 5.5kW (25% of 22kW). So "watt for watt", assuming an average usage of around 5kW, the fuel cost doesn't seem to be much different. Safety will also be an issue for many people. Not only safely connecting the genset to what it needs to power (which unfortunately many people do not do safely), but also fuel handling. At full load, continuous usage, you would be refilling the EU6500 every four hours. I assume oil changes would also be fairly frequent. Clean power to run lots of computer equipment is also important for me. I know the better portable gensets have pretty clean power now, but a lot of them still don't compare to what a good standby genset will produce.
A lot depends on where you live. It's almost a guarantee that if I have a multi-day power outage, it will be during the summer (100 degrees, 90% humidity) due to a hurricane. That means I will really need/want A/C. Unless I'm running window units (I'm not), a portable genset won't help me with A/C. If it weren't for the A/C (and "optional" electric oven), I could get by with a 7kW genset easily for virtually everything else if we are reasonably smart about usage.
Excluding hurricanes, it would be very unusual for me to have a power outage longer than five hours, and I usually go several years without one that lasts more than two hours (unless a hurricane hits). I work from home so it's important that I have convenient backup power, and it really is convenient since it's virtually automatic (when everything works right). I've never owned a portable genset, but one of the concerns I had about having one in my location was deciding when to put it in use. If I have a power outage that isn't due to a hurricane, it's probably due to a storm blowing a tree over on a nearby line, or a transformer blowing (again, due to my location). You don't know if the power will be out for five minutes or five hours and you don't have any advance notice, so the big decision is whether or not you break out the portable genset. Murphy's law says the utilty power will be restored within five minutes of you starting the genset, so you always hesitate. And it probably occured at 4:00AM during a thunderstorm. Once, after being without power for about 18 hours following a small tropical storm, and not having any idea how much longer the outage would last, I decided to buy a portable genset. I got it home, uncrated, and was literally seconds from putting in the gas when the utility company trucks drove by my house. Power was restored in less than an hour. Yes...I returned the genset since I hadn't put any fuel in it. That was Lowe's policy at the time.
I can certainly see how some/many people would consider a whole house standby genset an extravagance. But then some people consider $500K houses (housing is cheap in my area), $50K bass boats, $50K trucks/autos, $5K TVs, etc. as extravagant, also. As long as they can afford it, to each his own. After having a genset for the aftermath of Ike, my wife would refuse to live in a house that doesn't have a similar one (again, assuming we could afford it at the time).
But...you are absolutely correct. They are not cheap to run when compared to utility company power.