Sometimes 1 million is too much and sometimes 100 million is a steal.
Personally I think it's crazy to pay these money for players like Sanchez, Neymar, Aguero, Hamsik, Cavani, Pastore etc, who are yet to prove themselves at the highest level. But it's the market that sets the price and the teams know the best what do they expect for the money. Will Barca be right or wrong (as they were with Zlatan) is yet to be seen.
It's easy when you have the money. Teams can freely gamble. If they lose it won't be a biggy but if they win it will be a jack pot.