2002 Other Mitsubishi Models clicking noise/service engine s

Engine problem
2002 Other Mitsubishi Models 4 cyl Wheel Drive Type Mirage DE Automatic 112725 miles

my father had been driving my car for several months. This past friday he came to pick me up and a loud clicking noise was heard. So we parked the car once we got to his house. My boyfriend used to work on cars and said he would take a look at it in the morning. I drove it over there. Well as soon as I started it up, she acted like she wanted to turn off, and the service engine soon light came on. When I got to the house, he checked her out, he said he doesn't know for sure what the problem could be. But he does know it is going to cost a lot of money. I need to know, for sure. It depends on getting to and from work. So any suggestions would be helpful.