alt Hacker NewsFirst, have you purchased a bicycle? "High quality" bicycles start at $1,000. (quality dimensions = weight, comfort, durability, flexibility)
Second, small scale manufacturing is expensive.
Third, large-scale manufactured wheelchairs have the same problem as the rest of the medical equipment world: prices are subsidized/inflated by insurance.
I've only ever owned fairly cheap commuter bikes like Specialized. But even then, the quality and the comfort were OK. I guess in this case, small scale and configurability makes the biggest difference in wheelchairs vs bikes.