There is actually an entire segment of the cycling industry that has sprang up around catering to this demographic, urban commuters who want something functional and hip looking and are willing to pay the premium, but don't need a $1000 mountain bike for their trip to and from work. I have not taken a full survey of every bike commuter I see in my city, but I feel confident in assessing the cost of their ride falls under or just around $800 (assuming they bought brand new and not used, I think less people tend to buy new).
The amount of these hip cyclists grossly outnumbers the amount of "prosumer" cyclists (spending $2,000 on a carbon fiber bike) I see on the weekends riding trails. I would imagine these numbers are inverted in the suburbs, where you wouldn't find as many bike commuters, but the suburbs are also lower density than a city and therefore fewer potential bike riders to compare with.
EDIT: Also your point about middle class incomes and their effect on how much a consumer can afford to spend on a bike doesn't square with economics. I see your general concern regarding middle class wages not keeping pace with economic growth, but if a bike is essential to someone's lifestyle they will find a way to afford what they need.
And on a related note, many city dwellers are starting to give up on the concept of owning a car, favoring their bike or public transit or ride shares as a means to get around. Do you know how many bikes you could afford if you sold your car and no longer had to maintain its upkeep/insurance?
