How much is a second-hand Tesla worth?

As the popularity of Tesla cars continues to grow how much is a second-hand Tesla worth today? Even the forthcoming “mass market” vehicle will be priced in excess of $30,000 so buyers will want to know what they can expect from the second-hand market.

Do you have any ideas? While the batteries are guaranteed for eight years the warranty on the car itself is significantly less. Is this going to cause a problem?