Why would someone else invent it? If people decide to stop paying for the machines, or at least stop paying enough for him to suitably benefit from making/obtaining & maintaining the machines, why would anyone else fill in the gap if they're not going to benefit either?
Such technologies are common: per-unit and per-use cost may be low, but price of reaching that cost level may be extremely high. Integrated circuits are individually very cheap (!), but the machines making them cost $billions - they're not something you are, on your own, going to construct just so you can have an iPhone. iPhones exist because Apple put enormous money into making their components in such volume as to reach commodity cost.
Mr. Myne's machines may cost just a couple dollars a day to rent & run, but may have cost a billion dollars to produce to achieve that cheap cost - heck yeah he wants 4x retail price thereon because he needs to earn back that billion dollars and make enough additional profit to make the whole enormous activity worth his while.
A thing is worth exactly and only what another is willing to pay for it. If people will pay $8/day for Mr. Myne's machines, that's what it's worth.