The price is pretty darn cheap. I design / test products at my company and I know when I go over to our machine shop just how much goes into do a run of parts. There is also the design cost, the certification cost … believe me hydrostatic pressure vessels is not something everyone has out in the garage etc.
When I was a whole lot younger, I used to wonder why XYZ cost so much money in my opinion at the time … once I got into manufacturing etc. I got a grasp on things.
Also, it is not “just an acrylic tube” that you are buying. You are buying one that comes with a certification to actually work.
Ok, done ranting … I haven’t had my coffee and donuts yet!