Used bikes are not usually worth much, but the present supply shortage may help you.
https://www.theproscloset.com/
This place sells a lot of high end used bikes. Look around there, and see if you can find similar to get an idea of price.
A 6yr old bike is going to likely need new tires, tubes, cables to get going. They do not like to sit.
Good luck finding it a new home
gary