Oh, lots of ways cheap gas would help me afford a flat! First of all it takes a ton of energy to build a home, so housing would be fundamentally cheaper. Then, every month, I'd be spending less money on heating or air conditioning. I'd also be spending less of my own money on transportation (either through less gas costs, or buses/trains being cheaper). Then since goods are cheaper at the store, I have more money to spend at the store.

There is one mode of transportation that is currently REALLY cheap and that's huge ships. That's why we import so much from China -- sending a huge ship across the ocean is really cheap. If all forms of transit were that cheap (trucks, flights) the world would be very different.