What's the depreciation on a new bike these days?

I've never sold a vintage vintage bike (Lotus) for less than I paid for it, even the Lotus Legend that I bought in 1980 is still worth what it cost new and I've used it for decades.

Many vintage steel bikes were usually designed to last a lifetime (Lotus even had a lifetime warranty on their frames), the disposable-upgrade-to-the-latest-iGadget-mentality hadn't yet become the norm.