Please could someone help me with a rough value for this Trek bike?

Hi, apologies in advance as I don't know much about bikes.
Sadly my father died a few weeks ago and I now have the difficult task of sorting through his belongings.
He kept this Trek bike in his shed – looks like it's a ZR9000 Custom Alloy if that sounds right? I'd estimate it's about 10 years old but I don't know exactly when he bought it.
Please would someone be able to advise on a rough value for the bike – I'm in the UK. I'm assuming it's not worth that much but I've tried looking online on Ebay etc and haven't seen one that looks the same.