NFL referees have one of the most high-profile, thankless jobs you can imagine. To do their job well is to operate in anonymity while listening to the constant complaints of players and coaches. To mess up just once can inspire multiple articles about how you screwed an entire team and fan base and everyone knows your name.
While NFL referees don't make as much as players, they still earn a very decent living. Especially when you consider they only work about half the year. According to a 2016 story on Money.com, referee salaries were around $173,000 in 2013. The most recent figure we can find is a mention of $205,000 in 2019. Plus, there are bonuses for things like working playoff games ($1,500 to $5,000) and something like $10,000, $40,000 or even $50,000 for a Super Bowl. So if the NFL gives regular raises you can assume the average salary is creeping towards a quarter-million annually.
Again, none of these figures appear to be officially reported or released anywhere. Yet we know the details of most NFL player contracts right down to the language about how often certain guys can play video games.
Maybe if the NFL had some more transparency with officials' salaries, the public would have more confidence in referees. Or maybe people would say they were underpaid. There's really only one way to find out.