It’s cheap because it’s a risk. You take a player like Lucas Alario, also came from River Plate, a striker who scored 22 goals in 47 games for that club and left for Bayer Leverkusen in 2017 for more money they we’re supposedly paying for Julian (who has 23 goals in 57 games at River) at an older age. Alario was seen as a major player in South America; he scored in the Copa Libertadores final which RP won and also at the Club World Cup; a recent poll by their fans elected him as their favorite centerforward the past decade with more than half the votes; but at Leverkusen, he has 36 goals in 102 games and is currently Patrick Schick’s sub and doesn’t play much. He has an agreement to already come back to South America this window to play for Brazilian club Palmeiras and it’s pending on Leverkusen finding a replacement. Probably dreaming of World Cup but with 9 national team appearances and 3 goals it’s not going to be more than just a dream (Alvarez has five national team appearances and zero goals). European football is a big big step for a player used to South American football and why you can’t count on them to come in and fit in right away. The best striker playing in Brazil (and South America) today (Gabriel Barbosa/Gabigol, from Flamengo, who recently received an offer from West Ham turned down by the Brazilian club) also flopped at Inter and Benfica but is a king here.