For me, it's pretty obvious. Any bike I commute is has to be all-weather capable and convenient to use. That means a chain guard/chaincase, fenders, dynamo lighting, internal gears, and drum breaks are mandatory. Otherwise, it's not useful. All this implies at least $1,000 as a starting point. Mine was well above that and I could easily see $2,000 or more, adding in a 14 speed Rohloff to replace my current Nexus 7. Parking at my office is $20 per day, so any imaginable bike is chump change. The bike has provided daily transportation for nearly 20 years, so it amortizes out quite well.