A Merlin’s lifetime run-time, even with 25+ reuse launches, is just a hair over two hours (162 first stage time times 25 times two for the static burn). That’s assuming the high reuse stages keep all the engines even.
There are likely some compromises engineers can make when the engine is only running for that amount of time with refurbishment in between each 6 minute runtime.
A Falcon 9's Merlin 1D engine is reported to cost $400K. Its jet kinetic power in vacuum is 1.5 GW, in an engine with a mass of ~500 kg.
$0.27/kW is insanely cheap for a heat engine.