According to transfermarkt, about £63m - but that is a complete outlier, and £20m+ more than their next highest transfer.Unless, as you say, it’s any one of Real, Barça, Bayern, PSG, or Juve.
I’d also add both Milanese clubs to that - how much is Lukaku?
Then in the tier just below that, are clubs that can and will do it *occasionally*, those would be the likes of AS Monaco, RB Leipzig, Shakhtar, plus any wildcards that do just come out of the blue and find money ‘down the back of the sofa’.
But that’s five to seven A* tier options in Europe, plus a handful of A- tier options.
Not that domestic transfers should be ruled out.
AC Milan have never even got near those kind of figures - their record is £36m. Monaco's is under £40m. Leipzig around £30m.
I think a lot of our players are being quoted around the £50m-£60m mark, probably because of all the £50m transfers in the PL, but that would be close to an all time record for all but the biggest of Champions League clubs.
These clubs are not going to be stumping up record fees for defenders/midfielders in the age range that we're selling.
Domestic transfers are obviously where the money comes in, but I get the impression we aren't as keen on selling locally, and our want-aways less keen on staying in England.