Don't pay extra
You can buy any external HD back-up and pay $30 less by selecting one that doesn't say Apple/MAC on it. Then just reformat the drive and voila you're all set. I used a Seagate Free Agent 250 to migrate my files from PC to MAC then when I was done I reformatted and now use it with Time Machine as my external back-up. Thank you to the Best Buy guy that recommended this (wherever you are).