For the amount of hours a week I spent in Sync for Reddit and the price I paid then for removing ads, I feel that 20 euros is cheap to remove ads in Sync for Lemmy and would have paid more.

However I understand the price might feel steep up front for new users. An initial trial without ads for a short while might be a solution, where users only start to see ads after using it for a bit so they can test run the app without being disturbed by ads.