A small run production is sure expensive. Remember "Das Keyboard" ? It was all black keys with no print. It did cost more than double than an ordinary keyboard. I'm guessing maybe only 10.000 were made, and I don't think the "inventors" got rich. A lose BTC replacement key top would be cool and cheap to make.
Key mapping would be a custom character map and font, not hard to do.
Wut? Das Keyboard is still being made and rather popular, judging by number of mentions in places that I frequent. It cost 13x more than ordinary keyboard (ordinary kb being $10), but if owners are to be trusted, typing experience is infinitely better. It's a little weirdo but what proves more that you're ultimate hacker if not blank keyboard? Pair it with Dvorak layout and your greasy hair and body odor can't repeal chicks fast enough.