I'd love to be able to sell the Half Keyboard for $99 or less, but for a product to exist, it has to generate enough profit for it to be worth keeping around. There are 2 ways to do that...
Products with big markets, for which there are lots of customers, generally don't need to be very expensive. You don't need to make as much profit on each one, because you're selling TONNES of them.
For products with very small markets (like the Half Keyboard), you still have to make enough profit for it to be worth it. So, the only option is to sell it at a high cost. If enough people agree to pay that higher cost, the product gets to continue to exist. If they don't, then it dies and disappears.
If you are a disabled person, and you rely on typing for your livelihood, then the Half Keyboard is extremely cheap. It's not a consumer item. It was once, and it sold at a much lower cost then, but then the market shifted, and the only way to keep it around was to raise the price. It was either that, or let it die.