You can count the number of successful signings that have cost mega money on one hand. Tevez, Aguero, De Bruyne, Silva, Yaya.
We signed 3 of them when we weren't in the Champion's League and Aguero signed when we hadn't won a Premier League title.
Cheaper hungrier players have always been the best bet, which requires better scouting. Hart, Zabaleta, Kompany were all signed for peanuts. Mahrez was signed for peanuts. In 2010 whilst we were spending hundreds of millions on tripe like Adebayor, Dortmund bought Robert Lewandowski for €4.5m from Lech Poznan.
The myth that you need Champion's League to attract the best is a myth, we aren't going to sign Messi regardless and what good was Champion's League when we went for Pogba last summer?