With the extra wear you would put on the car for your "generator", you'd probably end up being cheaper buying a proper gen set....
You can get all sorts of generators nowadays, they ain't all the big, stinky, smoky, noisy diesel ones of yore. Some that could easily run your PC are small and quiet enough to use in the actual house (but the fumes ain't so good, although you could duct that outside). With battery power alone you also have to think of how long the power could be out for, you would then need someting to charge the batteries up. I would get a small UPS to run things for a few hours, and then a small, portable, petrol gen set for when an outage lasts a bit longer. That should cover you until you get a decent solar setup, and having that gen set would no doubt come in useful as you could just put it into the back of the wagon and use it for other purposes as well if the mood takes you. Nothing wrong with doing something that gives you more options!