Radbaz, R. David Ibn Abu Zimra, addresses the question of what constitutes 'overpaying' to ransom a Jewish captive.
This episode gets into the economic and political realities of the 16th century in the Mediterranean basin, including the burgeoning slave trade, and the resulting attention to the great mitzvah of pidyon shevuyim, ransoming captives.
Here's a link to the responsum: https://www.sefaria.org/Teshuvot_HaRadbaz_Volume_1.40.1?lang=bi
And here's a link to the first part of my series on Rav Ovadiah Yosef's teshuvah on the Entebbe hostages: https://jewishreviewofbooks.com/contemporary-israel/14972/rabbi-ovadia-yosefs-and-the-halakhot-of-hostages-part-i/