Call a locksmith. Everyone locksmith has a site just like the dealerships do (I know because I deal with the locksmiths and I work at a dealership). A locksmith that is up with the new times should be able to retrieve a key code just like a dealership can and then can cut you a key. He would likely also need all the same paperwork to do it but just another option.

I wouldn't go to that dealership, they are charging because they WANT to charge for the code and that is rediculous. I charge $10 to cut the key, the cost of the key, and tax. Just have to have all the paper-work I need to file, and people still throw a fit over how much it costs. No dealership is required to charge for a code, just document that you are THE OWNER beyond a shadow of a doubt and log it in a filing cabinet in cause of an audit. Just a way to keep GM and the owners safe. No need to charge for the retrieval, takes 2 minutes.