20/month for every chat service I use is very steep. I'd be spending more on chat services than on mobile data + unlimited calling + landline + DSL + streaming services combined!
They actual costs are apparently about 1 USD per year per user. I usually at least double (usually more) my incurred cost when the donation is optional, to cover for those who can't or won't pay, but paying 240× the cost price seems wasteful as well when there are other nonprofits that can do more good with every dollar you give them (be it solving poverty, climate change, whatever you find valuable) rather than one which has mostly fixed fees