What is a reasonable price for an used Nikon D5100?

The poster hasn't given an offer, so I'm not sure what to throw out.
Apparently they used it for a month, and have decided that it's too advanced for them.
I would like to give them a nice price, but also don't want to shoot for more than they want.
I also live across the country from them, so i would have to add the shipping cost to it.

What do you think I should do?

Added (1). It comes with the body, the 18-55 lens, the bag, 8GB SD card, battery, batter charge and etc.

Pretty much everything that comes with the box.

Based on the fact that Nikon offers D5100s (w/ an 18-55 kit lens), refurbished for around $580, your offer should be somewhere around there - New 5100 kits cost about $700. Just get this instead - http://shop.nikonusa.com/....242455300

"What do you think I should do?"… BUY LOCAL! I will not buy a camera/lens without holding/trying it first unless it is from a reputable place like B&H.

The thing to be aware of is it could be broken or stolen (especially if the price is too low). If you read through Y! A, you will see a lot of "I dropped my camera" or "My camera got wet".It is possible they got in over their head with it, but there are a lot of untrustworthy people in the world also.

If the camera is only a month old, then more than likely they will want to recover most of what they spent for it.