The problems arise when you start looking for "proven" 15-20m players. If a player is currently at a sizable club in one if the big four leagues and available for that price, it's because they have been deemed surplus to requirements. No one is selling players they want for that sum anymore. If you're looking for someone who has demonstrated that they belong on a big stage, yeah: you're going to have to pay 30-40m, and even then there are no guarantees.
Now, players deemed surplus can certainly come good, but they are also more likely to be on fairly substantial wages. They represent more of a gamble for the simple reason that they become extremely difficult to offload if they come up short, and suddenly you're paying four people (two of whom aren't at the club) to do one job.
It's also worth noting that our individual wages are perfectly in line (maybe even on the lower side) with the norms for an established club in the Premier League. The problem is that we've bought poorly, handed out generous extensions to older players, plus whatever the hell we were doing with Forster. If we merely trim our squad size and continue to backfill with youth, we can actually increase the wages handed to our best players without too much difficulty. That was Cortese's idea: before PL revenues exploded, we were handing out some pretty juicy contracts as an inducement to the likes of Wanyama to join a newish PL club, but our wage bill overall was perfectly reasonable. It's only after we started to pile up backups that things got a bit chancy.
So, overall, I agree: we need to get back to what worked. Target young players in the Championship, in Scotland, in the Eredivisie, in Portugal, in Switzerland, etc who are clear standouts...with the latter four, perhaps with an emphasis on players who have performed at the European level. Ones who are on the radar of the big clubs, but just a little too inexperienced to be expected to slot in there immediately. Such players are going to be more affordable in general, we'll be a more attractive financial option without spending 100k p/w straightaway, and it gives us access to talents of a level that we really have no other route to acquire. I mean, we had one of the best attackers in the PL and one of the top three defenders in the world, at the same time! Granted, it won't always work out (Elyounoussi ticks all the boxes and hasn't exactly lit the world afire) and our scouting and recruitment will need to be top notch, but those things are trivially cheap compared with the benefits.