Second most expensive metal, more than gold, palladium and platinum.
Nah. Rhenium is way more expensive. In comparison Iridium is cheap.
The actual costs of the metal used in jet engines at the elemental level is pretty trivial relative to the build price of a multimillion dollar turbojet. The bulk of the material will still be steel, titanium or ceramics while the more exotic elements alloyed in them are measured in single digit percent or even at parts-per-million levels. It’s the processing(precision alloying, tempering, annealing, machining) of the metals/ceramics to create high precision parts that account for the bulk of the material costs in building jet engines.