Not even a BMW, you’ll pay that at 21 for almost anything with full coverage. That’s honestly not that bad. I’d bet you won’t find anything cheaper, anywhere for a bmw policy.
It’s what you have to deal with. If you want the car, you have to pay for it. 21 is right in the sweet spot for the highest risk factors.
Something is up with your setup. Sounds like the undervolt is causing issues, like others have said.
Idle tempos are great, but what are the temps under hard loading? That’s what matters. If it’s crashing under load, it could be overtemping. Don’t assume your cooler is OK. If it were mine I would take it apart, clean it, and apply a Thermal pad rather than paste. I have a 13900k as well, with a 280mm AIO. I use a contract frame and use a Thermal pad instead of paste. I can run it at 5.5ghz all day long, and even such hardcore games like CB2077 or DCS in VR run in the mid 80s.