Last year, I bought an 8GB iPhone 2G off eBay for around $60. Had a crack on the glass above the screen area (not on screen view, just above), and the seller showed the serial on the auction. Checked it, asked and made sure he never taken it apart or had a 3rd party fix it, then bought it.
When I got it, I pushed a request to Apple for battery replacement, $80 (this was before it became considered obsolete). Sent it in with the box they sent me (I kept the SIM removal tool they included though!), then got a pristine refurb back a few days later, wrapped in plastic. However, after playing with the one I had originally purchased before the swap, I realized it was impractical for me to keep, and I decided I could not retain my interest in it. I put the refurb up on auction, plastics still intact, and sold it to a kind lady in Canada through eBay for $320. I had the original phone unlocked through AT&T before the swap, so I assumed the replacement would carry the unlock as well and advertised it as unlocked - I never activated it though, only powered it on to see the connect to iTunes logo come on, but left plastics on. Buyer received, and left me positive feedback, so I assumed all went well with the phone unlock.
Sometimes, I think back and wish I had not sold it. But, I look at my current iPhone, and smile at the progression of technology, how far the iPhone experience has come, and how much it has changed.

Sent from my iPhone.