As long as these lessons are available here, they are always going to be free. This is possible only because of the support provided by the community that has risen up around it. Through Patreon, hundreds of you pledge a few dollars every month, both to give back an amount you feel is fair (or affordable) for the resources made accessible here, and to help keep them around for those who can't afford to do so.
In addition to this, pledging through Patreon also makes you eligible to get your homework reviewed by me (there are different tiers for different lessons). Up until October 2016, I did this for free for anyone who wanted their work critiqued, but eventually the workload became too high. I can't promise that the tiers will remain where they are (as workload increases, I'll find various ways to decrease it). That said, there will always be free, community-based solutions for getting your work reviewed. This is really just for those who want to make sure that the advice they're getting is entirely in line with the lessons and their intent.
So! Long story short, if you've got a few dollars to spare each month and have found these lessons to be useful, your support is more than welcome.