While what could well be the panel used in this is cheaper[1], there's obviously consideration due regarding whatever device is driving the panel, making the frame/mount, and coding the software to drive it, etc.
You may be able to get a larger panel for the same sort of price[2], but there's something to be said for having a finished product that's fundamentally plug-and-play... which is arguably a different market to a "buy the components and make one yourself" crowd.
I have a similar thing running using a Zero WH and Inkycal. The screen I have is the same size (7.5 inches) but you can use bigger ones too. I didn’t want to shell out more money initially for a larger screen, but I may upgrade it later.