Is that true now, though? I mean most of the biggest signings, in terms of transfer fees, have actually been foreign players - we just shelled out €100m for Antony and €65m (or something like that) for Martinez. These are massive sums.
Barcelona have so many I can't even be bothered to list, but none of them have lived up to expectations. Real Madrid just shelled out €100m for Tchouameni.
It isn't particularly foreign players who are cheap; it is players who are completely unknown. Vardy - £1m ; Robertson (I know he is Scottish, but still makes the point) - £8m etc.