"But you could buy a used car for that much"
is the common refrain I hear. Yes, you could buy a cheap car for that much, and then immediately have to dump in at least $80 a tank for fuel.
The concept of using a bicycle instead of a car is just so foreign, that I think most American without active inter-cultural experience, say, living in a foreign country or at least multiple areas of the US, are not going to really understand how that would even work without having it spelled out for them line by line. Unfortunately, I fear that the people most likely to fall into a cultural homogeneity are low income, for exactly the reason that uprooting oneself is expensive.
When I go line-by-line explaining how car-free or low-car life is wildly less expensive than normal commuting, the main reply is... "Yea, that's stupid. Nobody is going to do that." I hear this in San Francisco, where anyone can trivially walk down to the wiggle and watch literally thousands of people every day commuting by bicycle.
At this point, it seems most people won't actually approach the subject rationally. People don't do it because it seems mentally ridiculous to them, and honestly, once I can get people out on a bike, they suddenly think that it's actually a really nice way to commute.