$300 is a little steep. You can get those keycaps that will fit on any cherry MX switch keyboard for $80-$100. Add a TKL keyboard (one without the number block) for $80 and you have your desktop typewriter.
$300 isn't out of the ordinary, particularly when you throw in a custom metal base and effectively one-off production costs on top of your $200 starting figure.
The Ergodox will cost you nearly as much in materials, more pre-assembled.
The Ergodox will cost you nearly as much in materials, more pre-assembled.