Huh? When did flex-PCBs get so cheap? This may be easier for a project I have in mind than my previous thoughts, if I can get the power rail tracks sorted in 2l for the available thickness. Yes, there will be a lot of LEDs.

Cooling may also be an issue of course. 

 @d4b81373 so cheap I'm tempted to dive down a rabbit hole with a flex PCB project just to prank someone.