i am buying a cheverolet lumina 2006 and its cruise control doesn't work , what can be the problem? is it's repair costly?

I would check fuse first. Then I would check the brake pedal switch. If standard trans also clutch pedal switch. These switches have to be made in order for the cruise to work properly. Hope this helps.

Also check the attached vacuum lines and check valves. Do a vacuum test on the vehicle before you buy it. A vac test can tell you a lot about the health of the engine. You may be able to borrow a vac tester from AutoZone. I believe it's called a MightyMite or something like that. It comes with instructions. I have cruise on my 90 Lumina. When I bought it, it had a vac leak, and the ac/heater vent doors wouldn't work, nor the cruise control. Good Luck!