Is that true? I guess what I mean is, is it $40B if you are trying to replicate the scale of a TSMC fab? Or could you do it for considerably less if the fab is initially designed to the needs of single customer (Apple)?

Closer to $40B for some of the latest fabs from TSMC you're seeing, yes. While there could be huge simplification in SoC and packaging processes if it was focused on a single product, Apple's needs will likely still be about having cutting edge processors, so it would still be pretty high even if they were to just buy TSMC.