I've been thinking about the cost of materials in that, and it's probably less than what you'd think.

If you knew what you were looking for, you could probably source all the bits for a couple thousand, however where China wins is labour cost.
I'd guess there's probably only £2-300 worth of metal in that, and at most a couple days welding to weld it all together, that's provided everything is cut ready to weld, which if it's done on a half decent plasma, or even laser, it should assemble with minimal issues.
Once your welding is done, it's just a case of painting, and assembly, finished of with a little bit alignment work (that's provided the welder has managed to avoid distorting everything...).

I'd like to see one up close, and to know if there is any kind of internal bracing, because if it's just a big open box, you could have one big resonator. I'd like to think given the reasonable looking exterior design, that will of been covered, but you never know.