Does something like $500k/year sound outrageous? Even if they employed 100 officials, the NFL would be spending $50 million on officials per year. They make $9 billion/yr, and pay the commissioner close to $40 million/yr alone. $500k sounds like it would be more than enough money to persuade the guys doing it now to give up their other career, and would certainly incentivize a guy just out of the game (college, pro) to take up officiating as a career, (or anyone else, for that matter).
The NFL could easily just put together an officiating school, or something like that, where they train guys and see if they are good enough to do the job in the first place. Getting actual NFL game experience would be the one thing they couldn't do, but it's nothing different than hiring a new official. Guys that make the cut move up to doing preseason games, or some other games to get some game experience and see how they fare. Most of the guys would already have experience as an official at a lower level of some sort to begin with.
Who knows, maybe this idea is completely ludicrous and makes no sense. To me though, I'd imagine the NFL would want to have the best officials money could buy, and would want to pay guys who can do the job as well as training them year round on what they want from an official.