That's not 1/3 of that 35 to 40k. The employer pays the fee, not the employee. This is very important. We don't want you to make less money; in fact, if that was the case many people who are already in highly paid jobs would not do it (myself included).

Funded startups that are looking for the top talent, at any cost, are the ones that I assume will benefit the most. For them, 1/3 of the 1st year salary is an investment. Better pay that rather than having to have the position open for 6 months (time is money). Hiring is extremely hard, and the people you want to hire... are by definition almost never looking for jobs. These are the same people that are attracted by the idea of spending 3 months mastering a bleeding edge technology.

From the company, not the participants of the retreat! That percentage is also not unusual; 1/4 - 1/3 of the first year's salary seems like a pretty common range. Who would you rather have your future employer pay that fee? Some annoying headhunter, who only connects 2 parties or a skill-boost camp that supports your growth as a developer over several months. Just my 2 cents.

My answer was referring to your comment that you didn't know what the average salary of a junior-to-senior developer in Germany was.

Also, 35 to 40k sounds really on the low end. I don't think I know anyone making that little. And this is Berlin, where salaries are lower than in the rest of Germany. 50k seems to be rock bottom for a seasoned front-end engineer, more for backend, even more for specialty stuff such as data science.