The other source is ebay. I got a generic third party (from china) 250 gb hard drive for $60. I made a search for sources from USA so that the shipping would be faster. I transferred all my files via a 16GB usb drive. Was easy to do considering I was moving from a 20GB hard drive.
Lastly, you might want to utilize the "transfer license tool." This is meant for when you move your content to a new Xbox 360. I did it because I had content assigned to 4 different xbox 360s from my RRD experiences. Now all my license are tied to my current xbox 360 and, if I'm not online, I can play all my content (especially my rock band music).
Good luck!