Why not Ebay? It's a great place to get a good deal on new/used/old stuff. People answer with Ebay when other people ask questions like this because it's a great place to shop, if you are a smart (and wary) consumer.
Use Paypal or money orders to pay for items, look at feedback (and last few months of available comments), rating, and location.
You have said "pretty expensive for a person to afford just to listen to music", so why do you need an Ipod?
For what you are paying, you can get a PSP which will play video, music, games, display photos, and let you surf the internet. (there's also very reasonably priced mp3 or media players (that include video/images) for what you will pay for an Ipod.