The mechanic that checked and serviced the car.

The mechanic that checked and serviced the car said that the hose that comes into the radiator leaks and so I need a whole new radiator. (The radiator light had come up on the dash board and I added some coolant the other day). He said he had fixed the leak in the hose going away from the radiator and it is good for now but watch the temperature.
I asked if if I need to give him notice if I am taking the car in for him to put in the new radiator and he said "No, just bring it in anytime and we can do it on that day" which makes me wonder why he doesnot have to order the radiator when he said I need a whole new one. He was going to charge me $550.
Please advise.