For anyone who wants to build a 13" retina cintiq:https://hackaday.io/project/4765-megapixy-a-13-retina-class-screen-on-a-boom-arm
this open hardware project uses the 50€ screen of a chromebook pixel.
It has a 3:2 aspect ratio, a high resolution and is definitely cheaper than a macbook screen (and also easier to use. including a good datasheet).
I also like the aspect ratio (tried this ratio on a friends surface pro 3 and it's very good for drawing. ways better than 16:9).
The person who designed this also said he has some spare eDP cables from a Chinese seller (the cable that connects the screen to the converter board).
I won't build one myself as I already have a cintiq and for a normal monitor 13" is a bit small (I'd love to see a 22" monitor with this resolution and 3:2
) but I can assist anyone needing help (as much as it is possible over the internet
if anyone of you lives in Vienna I could also help physically