You're going to have to get a cable modem through whomever you (duh) get your cable. I had a friend send me a wireless router that she fixed up, but you can try newegg.com because I strongly doubt craigslist or Goodwill will be helpful. Although, I'd have to find out exactly what my friend did since she set up the network name and password for me. Feel free to message me if you need more help.

Oh, and I'm a recent Macbook convert. Best laptop I've ever owned :-)