Why do these cars like taking money from your wallet
Because its 11 years old now, and any car needs fixing at this age - especially depending of mileage, use and pre maintainance history. And alloy radiators corrode both from the outside and from the inside if cooland is wrong type or not replaced with correct type.
As Anders say, the radiator is not expencive if you source one outside the Renault network. Find a Nissens radiator and it will be good for the rest of its life.