Ibrahimovic - first great European club - Juventus (came from Ajax) - well done Moggi!
Falcao - when Porto sold him, he was already famous and very expensive. They got him from River Plate.
RVP - arrived in Arsenal from Feyenoord, took years to develop
Aguero - started in Independiente, if I'm not wrong (and was already deemed to be a phenomenon - cost Atletico stg like 15M euros)
Etoo - Belonged to Madrid, was on loan to Mallorca when Barca got him
Luis Suarez - went to Liverpool from Ajax - probably cost less than 20M
Di Maria - from Benfica - 17M euro
Ozil - from Werder Bremen - 14M euro
Cristiano Ronaldo - from Sporting Lisbon
Henry - from Monaco
Cavani - Palermo
So... these are very good examples of now WC players who came from medium size European clubs, from weaker leagues - Portugal, Netherlands, Argentina. Nowadays it's very hard to purchase established WC players due to inflation caused by oil clubs. We have to find the gems when they are partially developed. Vidal and Asamoah and possibly Isla are perfect examples. Fee between 13-18M, young but experienced players who performed very well at medium size clubs.