Side note, the corvette crew is ~50% greater than the OPV.
It is also built for an entirely different environment and threat scenario.
A better comparison for the Arafura would be the German Federal Police Potsdam class OPVs.
They're 86m 1,890-ton OPVs directly derived from the Fassmer OPV80 sold to Chile and Colombia, with the design minimally enlarged and updated with extreme automatization (... with only 14 crew left onboard for the ship, plus an extra 5 if a helo is embarked). The class is intended for much the same purposes (sans MCM), and rather similarly armed and equipped.
Due to being part of the Federal Police as part of their contribution to the German Coast Guard their role is a bit more publicly decided and not open to questioning - there's zero intention or real possibility of ever upgunning them or using them for other purposes.
Budget for the Potsdam class was 60 million Euro per ship including 5 million for the 57mm gun onboard - or in other words
one-third the cost of the Arafura.
Main difference in cost drivers is
a) no flex deck per se - there is space reserve for something similar in the design around the boat deck, although on smaller scale, the South American ships can fit three TEU there -,
b) the design having been pretty much bought off-the-shelf from the catalogue, and
c) no tactical combat management system of military scale or related sensor or electronic warfare systems - rather "normal" radar, plus a relatively cheap fully integrated EO solution for fire control of the main gun. Besides general surveillance, policing and interception the ships may primarily be used in tactical insertion scenarios for effectively platoon-sized SWAT units with spare accomodation capacity for that purpose.