Lots of posts on HackerNews are adverts. That's what the "Show" tag is (partly) for. People aren't sharing their startups on here out of altruism, they want signups and conversions to paying customers. This isn't a show post, because the author didn't post it, and I don't think it's astroturfing. There are also plenty of posts for things that you can buy, because we (as hackers) think they're interesting. I think that kind of targeted advertising is OK.
On pricing, compare this to how much people charge for programming courses and textbooks. Not unusual for people to upwards of $200 ("Best Value!") for an ebook and some sample code. I have no idea who buys those, but presumably the payback is good enough and maybe for professional development it's worth it. For 14 hours of professionally produced content, even if incomplete, 22 Euros a great deal.
i literally laughed out loud when reading this comment. this entire site is an advert for yc and their portfolio companies. it's also a job board with restricted access.
@AlexMuir definitely deserves it to be at the top of HN with this project.