Badly worded title, should be "How to learn Ruby on Rails for $150". The author points out that it rightfully takes months of your time as well so depending what monetary number you value your time at, you could be very misled into thinking its better to do this than hire a professional.
It is better than hiring a professional. If you're in the business of building and running web businesses you should know the basics, regardless of how much your time is worth.