I have had some experience making prototype castings for an inventer or two.
The patent process is very costly and doesn't protect you and your investment unless you can sell it to a company that can go on with it and get it to market.
Someone can copy your idea and with a few changes in the design, patent it themselves.
One case in point was a tray of plant starters. The first design made the pockets in an inverted round cone design.
The next guy to copy the idea made them with a square cone shape.
The next made the with curved sides on the round cone. Several more designs were changed and all had a patent.
The idea can't seem to be patented, just the actual design of a part.
One fellow had already invested $20,000 . with a "Patent Company" and only had some paper work to show for it. I showed him how I could change 2 things in his design and repatent it for myself.
You might be better off contacting the company and sell them the design you have made.