Viewing distance sets the pixel pitch — not your budget
Pixel pitch is the gap in millimetres between LED centres; a P4 panel has roughly 4 mm between pixels. The common rule of thumb is that the pitch in millimetres is about the closest distance in metres at which the image still looks solid rather than dotty. A display people stand two metres from needs a much finer pitch than one read from across a road — and finer pitch costs more per square foot. Decide the distance first and the pitch stops being a negotiation.