TiPY keyboard is a one hand keyboard - https://tipykeyboard.com/en/home/ with their own TiPY layout, Regardless of having to learn new layout for typing the keyboard, The price is 350€ which although is relatively less expensive than other one-handed keyboards is still not an affordable keyboard for all.

If one is ready to learn a new layout for typing with one-hand keyboard then I think going for a DIY solution like https://artsey.io/ is the cost-effective way, Not sure whether this particular project - https://www.youtube.com/watch?v=dicYf7OiS3Q is currently maintained but there are other similar DIY projects out there.