I am thrilled that you like my prints, and I will happily give them to you for a donation.
I don’t earn my living with the prints, other artists do though. Therefore, a good starting point for the donation is at the lower end of the price range for professional screenprint monotypes (100€). This respects professional artists’ work, and I think it’s reasonable because both full- and part-timers invest a lot of passion, material and time into their work.