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The ones linked are nowhere near A4 or A5 in size. They didn't bother to even look up and suggested you realistic options. A4 sized e Ink panels at sample prices are, idk, $2k? Most engineers would be relatively price sensitive in those ranges.

It's not rare these days for people outside Asia to have completely broken mental math of engineering man-hours required for a product or how extremely subsidized the products in their hands are. iPhones can be bought for $499 not because they've figured out AI design and robotic mass production over in China, it's because they're leaving $2k-4k per unit on the table to be blown away in wind. And ultimately it's because that money is only nicety to them, not vital.

Which means, if you do the labor on your soil, your local economy will demand that amount to be on table plus some, counted, bound, and placed under a weight.