Then don't? Just take it to a store that cares about customer service and ask them to please do the transfer for free? I know of multiple stores in my area that do.
Or just buy a used cable and return it when your done (withing return limits of course).
GameStop often doesn't communicate these deals to it's employees until the day it starts. Most of the time these deals do not even make it into the bi-weekly marketing book or the monthly planner. In addition the prices in the stores computer listing do not change for these types of promotions...