I'm going to have an online machine shop build a part for me using a CAD drawing that I specify.

Typically, these parts are made of aluminium, but this manufacturer also mills parts out of these plastic materials:

• Polypropylene (PP)
• Polystyrene (PS)
• High impact polystyrene (HIPS)
• Acrylonitrile butadiene styrene (ABS)
• Polyethylene terephthalate (PET)
• Polyester (PES)
• Polyamides (PA) (Nylons)
• Poly(vinyl chloride) (PVC)
• Polyurethanes (PU)
• Polycarbonate (PC)
• Polyethylene (PE)

Polypropylene, I know, is the plastic used in water bottles, so I know that is not what I want.

This fabricated part will be used for the clutch cover on a motorcycle transmission and will have a raised section that needs to be tapped to allow attaching a gear shifter to, like in the aluminium version below.

I'd like something rigid and strong. Plexiglass comes to mind, but there could be a better alternative that I am unaware of, as long as I am not getting into something exotic that would cost more than aluminium.

Could suggest a good plastic for me, which would need to be oil resistant and withstand typical engine transmission temperatures.