A $150/hr freelancer who is busy for the year could reasonably expect to pull in about $100k gross (before any taxes, etc) assuming they take a few weeks off each year and bill about half their time or a little less. More if they automate a lot of marketing, have a local VA or someone doing the client phone calls, etc, allowing them to bill more. So the very successful ones are probably in the $150-175k gross revenue range before their taxes or paying anyone helping them.
I'm not saying @sidlls's implication that $150/hr is poorly paid isn't idiotic, because it absolutely is. Just pointing out that $300k will not happen strictly from trading 1 hour of work for $150 at any scale reasonable for a 1-person freelance shop.
Cue all the people saying it's "easy" or "just a matter of time" to get a $500k/yr job at Netflix or some garbage, but the truth is most software developers aren't going to work for any of the Big n companies, and will top out their comp around $125-175k cash and some RSUs that will be worthless 90% of the time. Even in Silicon Valley. So you get to make ~10% more in SV doing the same job you'd be doing in Minneapolis or Omaha or Pittsburgh or Charlotte or Reno for a cost of living that means you get to take home $500/mo in disposable income, sit in traffic for two hours each way, and pay one of the highest state tax rates in the country.
I'd rather make slightly less and have a maxed out 401k, Roth, be making double payments on my mortgage (how many people in SF can even have a mortgage, let alone pay it off in ~12 years, without being millionaires?), and be able to drive from my home to my office in less time than it takes the 2009 Patriots to make 5 touchdowns.
You sound really condescending. Less than 150$ is not "essentially free labor", and the people working for those amounts are not illogically choosing to do so. Even among developers it's a small fraction that can pull in the amount you are eluding to making. 150$ an hour works out to $312,000 yearly at 40 hours a week.