2005 Trek 1500 Road Bike price

A friend is interested in buying my four-year-old Trek 1500 road
bike. I'm trying to determine a fair price.

The bike has been ridden about 7000 miles. Has Ultegra-upgraded rear
derailleur, cassette and Dura Ace chain. it also has almost new Conti
4000 Tires. The condition is good with no wear on the seat and the
handlebars have been retaped in the last year. The only maintenance
concern is that it needs new brake pads.

Can someone help me estimate a price to propose or direct me to some
resources where I can research its value?