We have an old Honda EX 5500, which is a model that is not built in its current configuration any longer, and it is great........it will actually produce over 6500 watts at constant load, and is so quiet that if it is running in the garage you can't hear it in the house with the door closed. It will run for about 10 hours on a tank of gas, is liquid cooled, and portable to the extent that it is on wheels (It weighs around 500 pounds).
During the big ice storm here in Kansas City in 2001, we were without power for close to two weeks, and it ran the following:
Refrigerator
Forced air gas furnace
Freezer
TV, stereo, all the lights in the house
Microwave
Sump pump.
It would also run one surface burner on the electric range if we turned the furnace off for a while.
We were the only house in the area with power and heat, and we had the neighbors over to keep warm, and prepare meals, etc.
The problem that we encountered was getting gasoline for it during the outage, as the power was off over such a wide area, I had to drive at times over thirty miles to get my gas cans filled........
Back in the late 80s when this model was made, it sold for around $2199, so I would suppose that a similiar capacity model by Honda would probably run twice that much today, but you might find a used one somewhere, and if it needed repair, parts are readily available (but expensive).
Needless to say, I doubt that you will find anything with the capacity that you need for $400, unless you locate one that needs repair, and do it yourself.
doc