Mine would be:
- Doing an OU degree. It took 6 years but it was really interesting and the feeling of accomplishment at the end was worth the slog.
- Going on Mounjaro. I'm 30kg down and feel great.
Both cost a bomb and needed long-ish term commitment that took money/time that wasn't centred on the DC, but I'd say they were worth it for the improvement they made to my life.