I haven't machined hastelloy but that's some expensive shit. That seems like a poor use of that alloy though, but whatever lol as you said it's their money.

I recently did a reactor that was supposed to be 1200C at 30,00PSI and wanted to use hastelloy X (alloy used in nuclear reactors) for that, but budget made us use 316 at a stupid wall thickness and lower the pressure to 5,000psi @ 800C. Same shit but opposite.