This table is from an Ernst & Young study published in 2006. It lists the total costs of €2m in net wages for clubs from the 6 richest European leagues. While it is a 2006 study, it should still be representative.
The bold "Gesamtkosten" part is of interest here. As can be seen, Spain has a huge advantage with their '25% flat tax' (for foreign players). The same applies to Holland to a lesser degree, Spain and Holland have a lower tax rate for foreign players. France has a huge disadvantage - French clubs basically have to pay twice as much as their Spanish counterparts (for foreigners). In England, taxes are going to rise soon, so EPL clubs have to pay more soon also.
The bold "Gesamtkosten" part is of interest here. As can be seen, Spain has a huge advantage with their '25% flat tax' (for foreign players). The same applies to Holland to a lesser degree, Spain and Holland have a lower tax rate for foreign players. France has a huge disadvantage - French clubs basically have to pay twice as much as their Spanish counterparts (for foreigners). In England, taxes are going to rise soon, so EPL clubs have to pay more soon also.