What a layout cost to build, and what it could be sold for a few years later, are two totally different beings.
I have dismantled no less than nine layouts in my lifetime, no one would have wanted to buy them. Not because I'm a bad modeller, because I am a very good modeller. No one wants another man's empire. A used layout has to be one of the hardest things to sell. For a halfway realistic price that is.
I currently have three layouts, a British 00 almost complete, a USA Maine Seaport layout, built to be dismantle-able, 99percent complete, and a USA On30 portable layout 50percent done, could I sell any of them for a quarter of what they cost? No. Especially if time to build was taken into account.
Knowing the value of a layout is easy for anyone who has built one. Realizing that value in a sale - impossible.