I've only ever heard this name pronounced as PRY-uhm (to rhyme with "DRY-'em"), not PREE-uhm, even though PREE-uhm makes the best Greek phonetic sense. After seeing this site and a few posters stating that the pronunciation is PREE-uhm, I checked a handful of other sources- some online and some not- and all said PRY-uhm, not PREE-uhm. This name might be one of those ancient names like Boudicca that people can't agree on how to pronounce (and in her case, spell, too).
https://it.m.wikipedia.org/wiki/Priamo_(nome)
https://www.name-doctor.com/meaning/priam
https://meilleursprenoms.com/popularite-prenom/Priam
http://www.names.be/voornamen.html?met=Priam&sort=beldesc