[riho]

I'd look at it from another perspective. Committing to learning an entirely new language is a big undertaking, so ideally you want to make sure that the resources you're using are of high quality. In that sense, it costing money is actually a good thing, since it signals that this is premium quality content and worth spending your time on. Of course this needs to be clearly communicated as such, like Brilliant.org for example (at least their marketing communication focuses on the quality).