Did it stop working about the time you had the work done to your car (about 7 months ago I think you said)? Could be your mechanic didn't hook it back up, either physically or electronically. If so, take it back to that mechanic and have them take a look.
You can check the photo you posted in your other thread, there are two cables which are to the right of the oil filler cap and to the left of your red circle. One of those cables goes to your accelerator pedal, the other goes to cruise control. Check to ensure both of those are attached to your throttle body (on the engine side). Also, follow those two cables back the other way. One will go to the firewall and into the cabin. This is attached to your accelerator pedal. The other one should be attached to a diaphragm or electric servo. If a diaphragm, ensure this is attached to a vacuum source. If a servo, it should have power/control wires plugged into it. If you find a socket on it without a wire plugged into it, you've probably found your issue.
Cost on repair is going to depend on what is wrong and where you take it. No way to tell you over the internet.