2002 Dodge Intrepid Problem!?

[Pac]

I have a 2002 Dodge Intrepid. The engine light is on in my car and originally a mechanic told me I needed to replace the computer in the car. After a couple weeks, I brought it back and he then says he will do the wires. He replaced the wires and charge me 600 dollars. The engine light turned off. As soon as I step in the car the engine light came back on. So then he worked on it some more and then says I;m going to need a new computer. I told him I can't afford that and then he said he work on it some more. He worked on it twice. The engine light goes off, but comes back on soon thereafter. Now he saying the car needs a RPM. So now I'm getting real mad and told him I come back to him because I'm starting to feel like I'm being scam. Can anyone tell me what they think might be wrong and if they think I'm being scam? I know nothing about cars.