What about renting one from the local equipment rental shop if you only need it Thursday! Then if it's the wrong size - no biggie!
We ran a 2400 W one here for 6 years; that was enough to let you shower and go somewhere with power, without worrying about food, but not enough to run heat. If we turned off everything else in the house we could power up the home theater. This year, we went much bigger - now you can even run the washer and dryer and heat without anything going. But we lose power a lot out here - sometimes for two or three days at a time.
