https://pcpartpicker.com/trends/price/memory/ is better. pcpartpicker has the data.

You can see the SKUs they base the prices on by hovering over a data point, and the products just don't generally represent the market. Oftentimes the whole market is represented by some bottom of the barrel legacy memory, single stick in some warehouse. During the last years DDR3 and DDR4 haven't gotten as expensive as the current generations, and I think the memory compatible with current systems should represent the market rather than a Toshiba Satellite 4 GB extension kit.