problems

i have a 2001 ae maxima my engine light comes on at the same time with the brake light i got a new battery but i think it's my alternator i called the dealer they want $550.00 to put a new one in what do i do. i took it to a shop across from my house he checked it and said it was the alternators but how can i be sure and he said one of my fans behind the radiator needs to be replaced can i do that myself and also what are the steps to change the alternators(rough idea) he tells me he has to lift the engine and take off the motor mount to change the alternator some body please help me before they f---k up my car should i just take it to the dealer? thanks for the help people have a good day?