This is a part you would want to purchase at a auto salvage yard. Buying it from GM would cost plenty. Call around your area for prices.
What it would cost to fix your steering column depends on what is wrong with it and you did not tell us. The tilt steering column in my 1989 GMC Suburban became loose in the tilt mechanism. I was quoted as much as $125.00 to fix it, but I shopped around and got it repaired for $60.00. Unless your steering column has the same problem that number is probably useless. I would suggest you call several shops and get a quite to fix it.
The 2010 Chevy Cobalt Power Steering costs about $400.
The 2010 Chevy Cobalt power steering wheel will cost you about $400.
5000dollars
It is under the dash to the right of the steering column near the brake light switch. remove cover toward the fire wall look up . it is on the right hand side, it sets in a clip. pull it out much easier to change. It took only 10 min once I figured out it was not where the manual said it was. I spent about an hour before I went to the fire wall.
10 bucks
The wire in the steering column has to much strain on it and it snaped. Easy fix if you extra wire laying around. Just rip the steering column apart
Probably have to remove steering column which is not too difficult if you find a good book with diagrams. Then take column to locksmith. First call locksmith to see how much they charge. This should save a lot of money compared to having a shop do the whole thing.
If you do not keep your power steering fluid topped off, and/or do not change it once a year, your steering column will most likely start burning from friction of the steering rod and column. The best thing you could do is take it to a mechanic, to see how much damage you've done by not topping off your steering fluid. This is something explained in every owner's manual, but not often read. This is how most mechanics make their money, by people not topping off their power steering fluid. If it isn't looked at soon, then your steering could go out, and you could crash.
$60-$80
I have a 2006 Chevy cobalt and there was a recall to replace the electric steering unit. Check to see if it was done first.
There isn't much to diagnose. Either the electronic steering works or does not. You can check that the wiring harness or wires are not damaged, but when a power steering failure occurs with the electronic steering on the cobalt the electronic steering component must be replaced.