I've used CCleaner for years and would like to support it financially, but $20 a year is too much. That's the cost of an internet security software. I have 5 computers. If CCleaner cost $1.99 ($2) a computer, that would be a fair price. I bet only 1% of the users pay for the premium. I bet over 50% or more would pay $1.99.
G'day @alur and welcome to the forums,
the cost of anything will always be subjective.
one person's "too much", will be some body else's "that's pretty good" and another persons "that's cheap".
from a cleaning perspective, the Pro and the Free version offer the same outcome.
as you probably know, the Pro also gives you priority support, more monitoring options and the ability to clean all users of the PC from one spot.