This project will work with a 7.3" display just as well - they are £79.50! https://shop.pimoroni.com/products/inky-impression?variant=5...
Disclaimer: I am the CEO of Pimoroni :-)
For a product that is made for creators and DIY, AI generated imagery on the product photos doesn't feel right.
Yeah, the 4 and 7.3" prices are not bad, the jump to 13 is just large. That being said, the cost per area goes down, so it is also probably fair.