To go that route, you would have to start with rectangle stock and do all the work on a mill, or a lathe with live tooling. Expensive machines. For us, we charge $75/hr for our lathe and mill work. The doesn't include any one time NRE or tooling costs to get things up and running. And because there is two end, you would probably have two setups. Or one setup and turn the part. Still time. I would think a minimum of 20-30 minutes machine time. So just a rough estimate of $50/part that way.
The route I would go is get tubing, machine each end to the correct diameter with an o-ring groove. This can be done on a manual or cheap little CNC, even a screw machine. Then cut the ends at 45 and weld them together. Simple, quick and done. Probably about $20-25/part.
But if this guy can get them in under $10, I will buy a set or two. I don't have elbow issues either. But my dad did have issues that one broke as he was driving, lost all coolant, overheated the engine, and warped the heads. So for peace of mind, a metal one would be nice. And $10/ea would be the price point I would buy one.