Yeah, I agree Premier League/Championship players probably wouldn't be assed, its a stressful job, TBH I doubt they would be allowed to to ref in the UK anyway due to previous allegiances.
But I would some ex lower league or semi pro players that never quite made encouarged to give it ago.
Have any top refs even played county football?
Not that I know of but I suppose there might be a couple. Interesting contrast with cricket where most of the umpires are ex County players (I think playing first class cricket used to be a requirement but not now)
One of my former staff was the twin brother of a guy that refs at European level (based in Scotland and normally reffing in the MTL and an identical twin so caused a few issues for my guy on nights out in Glasgow depending on how the games had gone LOL) - going rate then (and this was a few years ago) for Europa league was around £5k per game plus expenses.