Your comment shows a lack of perspective.

Depending on where you live, $400 could be a good amount. OP could be living in another country where this kind of money could be very interesting.

Life is not that simple.

What if:

- He actually needs to do it for regular job or pure interest, so the time is already lost. This way, you kill 2 flies with single shot

- Hosting and other stuff can be done for $0 nowdays

What I learnt here (not really, just improved current understanding) is that people suck at deduction and resort to simplistic observations that have no roots in reality.

I used to think side projects / businesses needed to replace my income for it to be worth it. After I started getting into the habit of budgeting I started to realize that a even a few hundred extra bucks a month can go a long way. Since this is a one time sell product there's little support to spend time on (just give them a refund). The author also has organic marketing with SEO.

Depending on what you're doing there can also be significant value to being perceived as both an expert and an authority in your field.

author did not put too much effort into marketing as explained in the posts. the target audience was already figured out and the blog acted as a funnel... hosting is $0 as per author.

so yes, this is totally worth it as a side project.

Well, then, it would not make sense to publish a free ebook, would it?

This is a great point. It's $400 in sales per month. I'm willing to bet hosting, domain, any paid ads, any fees from leanpub, etc. makes up at least $100-200 a month. Probably be better to just do freelance/consulting on the side and make an extra $100/hr in a day.