Ah, thanks, I looked for that but didn't find it (the "donate" button reminded me of a one-off). I'd recommend changing the link name to "pricing" and A/B testing the recommended donation amount being $5/mo.
I don't know how much effort they've put into experimenting with pricing, but it'd be worth trying to increase donations, especially for such a well-designed site.
Never knew they had this, signed up immediately :)
Exercism is worthy of 120$ a year and worth its weight in gold. It has helped me learn Rust, Swift and Kotlin and I'll be forever greatful!