Congrats on getting the wife to go along with the generator. Mine was a little easy to convince. We have a usually full freezer and a fridge. On a long outage (1 day in the summer) you will probably loose all the food in both so that right there could easily be $500. And with our finished basement we need something to run the sump pump.
If you get a 220 unit and don't do a manual transfer switch, you can use a cord like this:
http://www.sears.com/shc/s/p_10153_12605_07107371000P?prdNo=6&blockNo=6&blockType=G6
It will let you split the 220 twist lock. The good thing is that the twist lock won't vibrate loose like a regular cord could. Just put 1 heavy load on 1 side the other on the other, etc. Try to keep it as balanced as possible .
One thing you might want to consider is how long you plan to be in your house. We plan to be gone by next summer (as soon as the basement is finished it goes on the market) so a permanent install is out. But if we were to do it over again 11 years ago I'd go permanent. By the time I add up the $600 for the generator, the $100-200 for the cords, etc, etc, I'm 1/2 way to the $2k for a permanent unit.
Think long and hard about propane or natural gas. You need just as much propane as gasoline and when run on propane there is less watts available as propane doesn't contain as much energy as gas. So you may end up with a couple large propane tanks that you need to get filled rather than gas that needs to be filled. And the propane place may not be open after an emergency. Natural gas would probably be the best option if it's available.
Don't forget Diesel as well. it stores almost forever and if you heat with oil, heating oil is a close substitute for Diesel.
Not sure I'd leave a portable unattended and running. It may grow legs, could have a gas leak and start a fire, sputter and die (bad as things can spike), etc. Ours I wheel from the shed to the end of the carport, point the exhaust to the bushes and chain it to the support of the carport. There's about 10ft from our window and more than that from the neighbors. You do want to keep the exhaust pointed away from the house and the unit somewhat away from the house. Also a battery CO detector or 2 in the house is a good thing.