Why is the Kawasaki Ninja 300 not part of this discussion? It gets around 70mpg, has a 300cc engine instead of a 250 and is one of the top/best rated beginner bikes out there. You should be able to find a 2014 one with ABS at a decent price. I just purchased one in June for about $3700 USD from craigslist. The ninja 300 has plenty of power to easily, easily outpace a car. It's a sport bike, but for a 15 minute ride it is plenty comfortable. I hit 80mph on the freeway if I'm not paying attention and it cruises along nicely at 70mph.
Most folks only change oil once or twice a year (about every 5,000 miles). Motorcycle oil is more expensive than car oil. You need to regularly lubricate your chain also, occasionally adjust your clutch cable, and tires wear out faster on motorcycles than they do on cars.
Don't buy anything too nice or expensive for your first bike. I'm 99.9% confident that you're going to drop it at least once as a new rider. The 250 or 300 CC bike is also going to be lighter and easier to pick back up than a 650. I say this because as a new rider I stalled mine trying to take off from a stop up a hill, lost my balance and let the bike fall (I remained standing). I was uninjured because I was barely moving, but pretty embarrassed. Other folks tend to wipe out taking curves improperly & slide off the road.
Don't just think about the cost and maintenance of the bike. I recommend a motorcycle safety training course. They'll teach you lane positioning and how to take curves & turns. Helmets are also expensive. You'll need gloves, boots, a riding jacket, and riding pants too. The boots protect your feet from being crushed if the bike falls on you. Sneakers/tennis shoes will result in broken feet. The pants, jacket, and gloves protect your skin from being torn off if you fall. The helmet is a no brainer and at least in my state/country it's against the law to not have one.
Anyway, hope this helps & best of luck! I'm actually creating a post very soon on a motorcycle-related subject.