Sources:

https://www.wsj.com/articles/viewers-dont-add-up-to-profit-f...

http://fortune.com/2016/10/18/youtube-profits-ceo-susan-wojc...

https://www.bloomberg.com/news/articles/2019-02-04/alphabet-...

While there's nothing concrete concerning how much YouTube costs and brings in, it seems to be generally understood that YouTube is an investment that hasn't reached profitability yet and only exists in its current state due to the fact that Google is willing to lose money on it in the mean time.