The major reason a cessna is so expensive is because the FAA certification process is insanely onerous. Look at experimental category aircraft for personal use - illegal to use for commercial purposes, but a better representation of what planes would cost without massive regulatory burden.

The FAA regs have some reason to exist, because planes falling out of they sky tend to be more disastrous than car defects - but they're also the biggest reason small scale air travel is still so expensive.