Well...my personal opinion, When it comes to owning a BMW, gas consumption is not an issue. It's all about looks, performance and handling. You pick the model and price to your budget, you go get what you want! I would think someone who is concerned about gas mileage would be happy with a protege or civic.
Having said that...BMW's typically are not that bad with gas consumption. I would even say they do pretty well with the performance they deliver compared to many other gas guzzlers that don't come close to a BMW's handling and performance.
2012 Porsche 911 GTS
2008 ford F150 Foose Edition