There is no set price for used camera equipment, however, you have to take into consideration that the sensor will only take so many photos before it goes out. As well, technology changes. How many megapixels is th camera and how does that compare to what is available today? Does it video as well? That is now available for most DSLR's today. Being that it was purchased used, you have no way to find out how often it was used. It is possible it was a photography enthusiast or someone who purchased the camera for a trip and never used it again.
My assumption is that eBay is going to come in a little lower than a camera shop selling used equipment.
As for the lenses, you should know what F stop they are. The lower the number the better. 2.8 would be wonderful, 4.5 ok, and 5.0 not so special.
With that said, I would offer anywhere from $20 - 35% of the new price, depending on the variables.