Bikes are like cars, as soon as it hits the ground, it loses 25% right away. Except cars have a much more efficient used market than bikes.

A brand like Colnago is just too esoteric to have a big demand unless you get lucky with someone who really wants one. So, I think anywhere between $1500-2000 is what I would expect realistically because that seem to be a sweet spot for people who are looking for new-ish carbon bikes. If the warranty is still valid and transferable, you may be able to get a couple of hundred bucks more.