4. Diego Costa, Atletico Madrid to Chelsea
At £32m it would be difficult to describe Costa as a bargain, but if the 25-year-old can replicate his form for Atleti last year for the Blues, then it will be smiles all round at Stamford Bridge.
The striker netted 36 times in all competitions in 2013/14 as his team won La Liga and reached their first ever Champions League final.