Reply to Macbook Pro Help

So I just recently upgraded my laptop to a new Macbook Pro 15" (Booyah), and i need to sell off my old one. My problem here is I have absolutely no idea what it's worth or where to figure that out, so I figured I'd ask you guys. I have a few coworkers who are in need of a cheap laptop but i don't know how much to ask for it and I don't wanna seem like i'm trying to rip them off or get screwed over myself.

It's a 15" Macbook Pro with an 80GB hard drive, 2 GB of RAM, 2.0 GHZ Intel Core Duo, in good cosmetic shape, and it comes with literally every piece of packaging, cables, and manuals it came with. It was purchased in June of 2006.

I was guessing maybe the $300-$500 range but like I said, I really have no idea. Any help would be GREATLY appreciated, thanks in advance!