I would recommend buying new, mostly because of the warranties. Saving $20-$30 bucks on a used drive towards the end of the warranty life just isn't worth it.
Get a credit card if you are too broke, or save up for one. One thing that is a valuable lesson for Hardware is that you simply can't skimp out on important components. Sure, you pay more upfront, but the performance, value and reliability is worth it and it will save you cash down the road. I know there are rare cases where you can buy cheap and luck out, but not worth it IMO.
EP, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS