> Is memory really that expensive? For 100$ I can just buy 16G, I suspect for most people it would be cheaper in productivity to add more ram instead of the production loss you get from not having enough ram.
It is not just the price of the memory stick. It also uses more power. You might need a more expensive server with more memory slots. It is one more piece of hardware which can fail and need to be replaced.
On the software side, the operating system has to use more memory to track all the available pages, and on 32-bit architectures this memory might have to be in the very valuable low memory area (below the 4G limit). Your memory management algorithms might also need more time to manage all these pages.