https://steamhost.cn/steamcommunity_com/id/imanmh/screenshot/2272696081031039568/

Hmm, I need to put some limits on the calculation of bills. I think it comes from mods that do weird stuff with value of items or smth. But some sanity checks on bills is next up my todo list...

Yea I think the easiest way to handle this is to first set a limit on the bill amount (can still be challenging because there can be expensive surgeries). And the ultimate fix could be to exclude the medical operations if the used items don't have proper value.
Glad I could show you the bug, I'm pretty sure you'll find a way out. Good luck.