Getting a key cut for my car?

I lost my car keys and heard it was going to be an arm and a leg to pay a locksmith to make a new one to fit my oldsmobile 98. Could I buy a key directly from GM with my vin num? I called the local GM dealership but Im still waiting on a reply. They have the key that fits my car on ebay but I dont think it is cut to my vin number... would this be even worth buying? Locksmith pros help me out