Like most things, when you px a camera you only get a percentage of it's street value because the trader needs to leave room to make a profit when they sell it on. You would (almost) certainly get a better price by selling your D60 privately - the for sale forum on here is a good place to start.
How much can I expect to get for my D60 Body, and how much can I expect to pay for a D90 / D80 Body?