Get a cheap bike that is nice to ride, 2 locks, and learn how to lock it up properly.
If you are commuting, I wouldn't pay more than $100 for your bike anyway. Unless you are biking 100 miles a ride, you'd be hard pressed to notice a huge difference between a scratched up steel frame trek you found on craiglist and tuned up vs. some carbon fiber precision instrument imported from Italy. My maintenance costs are taking it to the bike shop once a year for a tune up - $60 and they give me new pads. I haven't had a flat since I bought gatorskins, and even though I suck at changing them, an inner tube is cheap and takes less than 30 mins to change. Those dollar or two rides on bike share really add up if you start relying on it heavily.
I get that it sucks hauling in a bike on a packed subway, but in the u.s. that's only really a concern for commuters in nyc. Even L.A. is a bike utopia once you get comfortable with traffic grazing your elbow and cutting you off all the time; it requires thick skin, and planning your routes a little differently, but you will always be faster than a car in traffic due to filtering.