[Diti]

OP mentioned this is a “simple app”. They should follow the example of the author of parcelapp.net, which charges less than 5 EUR a year. That’s 50 k€ per year (judging by the ten thousand of reviews (4.8/5 star average) on the Apple App Store. Without taxes, of course.

More than enough to pay for server costs.

[latexr]

Worth noting that Parcel used to be a one-time purchase, and those who bought during that time are grandfathered in with a lifetime account.