I don't know that you can get the ign. cylinder out of the column without a key. I believe that is where you verify the key code? Scott will have to clarify, specifically.
The way GM usually does ign. cylinders is if the cylinder goes bad they re-key it to the key you have (OEM). So, if you provide a VIN they can make the key from scratch according to what the ign. cylinder is keyed. It costs what it does because of the chip in the key, plus they charge you to "look up" what the code is because I believe they are charged to access it.
Again, you may want to PM Cordell for the best answer.