Scout properly and sign CB's that fly under the radar for cheaper rates. Not every defender is going to cost 85m nor is every good defender going to cost 85m. Only the overhyped big names in the PL will command that sort of fee. Most other defenders playing outside of England in places like Brazil, France, or the Netherlands won't get as much exposure, hence won't sell for over 50m.
There are plenty of good defenders out there that we probably haven't even heard of, we just need to scout properly and we should be fine. Midfielders and attackers get most of the attention since they're more flashy players that have a greater impact in goals scored, whereas a good defender goes unnoticed to most viewers, thus gets less exposure.
If we're smart we can avoid paying such outrageous fees for defenders for the foreseeable future.
Yes, we can scout for players outside of La Liga and EPL.
But then, we did it a lot of times in the past with players like Christanval, Chyngry, Caceres, Brasilian defenders.
The only 2 foreign CBs in the last 15 years who were a success here (for a lower price) were Rafael Marquez and Umtiti.
Imo, a success rate with these kind of semi unproven players is 1/3, 1/4 or 1/5.
So, you can't just buy Marlon and put your all eggs in his basket.
Or buy Mina and do the same.
A problem with these kind of youngsters, who are unproven on the highest level, on NT level and Champions league is that you need to buy 3-4 of them to get ONE player who will be okish.
If you buy 1, you are most likely screwed.
But if you buy 3, then, how will you develop them?
You can't give a playing time to all 3, because a 1st team will suffer.
And if they don't play regularly, you'll get a new Semedo, new Samper and similar.
So:
1. if you buy only 1 player like Marlon/Mina, 80% probably nothing will happen
2. if you buy 3-4 of them, how will you develop them?
3. if you loan them, well, we all know what happens lately with our loans. People say that we picked either a wrong team or a wrong league, or that a manager doesn't play our player because he needs a player who will actually stay in a team in upcoming seasons
So, I am not against your proposal.
But how to make it work in reality?
And please, don't reply: we need to pick only 1 guy, in whom scouts are 100% sure and then go all in with his development.
You can't go all in for a 20-30M guy (And now even Sanchez is around 40-50M, right, lol?) and expect to go all in with a development of that guy from a weaker league and with zero NT, CL, La Liga, Barca experience.