Most cost effective/best way to drive a large array of panels (256x256+)?

[marcmerlin]

Funny you’d mention that, I was just making this post:

384x192 RGBPanel Matrix

Having fun with RGBPanels. I temporarily built myself a 384x192 display with 9 scan row RGBPanels linked 3 levels wide and 3 rows run in parallel. All running on an rPi4 with GitHub - hzeller/rpi-rgb-led-matrix: Controlling up to three chains of 64x64, 32x32, 16x32 or similar RGB LED displays using Raspberry Pi GPIO given that ESP32 or teensy can’t really do more than 128x64 on a single chip. My refresh rate is just above 100Hz on an rPi4. Realistically you can’t run many more pixels than 64x3…

512x512 could be done on rpi-rgb-led-matrix but the refresh rate would be unacceptable.
Realistically you can do the 384x192 I just did, or you can step up to 384x384 (half refresh rate), and then 512x384 (refresh rate will really suffer), and this is by having 3 busses running in parallel.