1998 Pontiac Grand Am My car is smoking

I bought this car in August for $800 and drove it for 4 days when it started running hot. I pulled over to the side of the road and the temperture gauge went down to normal. I started driving again and the temperture gauge shot back up then bottom out. I pulled into a gas station and smoke was coming from everywhere. There was an extremely large amount of green coolant leaking out all over the ground and you could hear a steaming noise. I went back the next day to pick it up and got half way down the road and it did it again. I took it to a shop and they say it is the intake valve cover gasket and that it will cost 550.00 to fix. Please help me, I think they maybe doing this because I am a girl and don't know much about cars.