$50/hr is VERY cheap. A decent developer in the Bay Area really should be charging at least $100/hr-- otherwise, they can just get a job and make more with less risk. Seriously good developers can charge upwards of $300.
For certain skillsets (including some that the OP lists), charging less than $100 / hr should probably include some justification or people will just assume you're not any good because you're charging too little.