The test of reasonableness is different for everyone.
I have no interest in cloud backup, or any other feature that incurs a cost to the dev. So why would I pay a subscription fee to "cover" those features?
If I like the app after sustained use, I might be willing to pay a one-time $8-$12 fee to remove ads/thank the dev/buy them a coffee
But I have zero interest in an ongoing subscription at this stage. There's just not enough value for me in spending that sort of money.