Grimes gave an interview on this:
"[Musk] lives at times below the poverty line," Grimes said, per Vanity Fair. "To the point where I was like, can we not live in a very insecure $40,000 house? Where the neighbors, like, film us, and there's no security, and I'm eating peanut butter for eight days in a row?" [0]
In the same article Grimes complains Musk wouldn't replace a broken mattress.
No idea how Much this shows Musk is cash poor, and how much it shows crazy rich person, but it gives a glimpse either way
[0] https://www.businessinsider.com/grimes-says-elon-musk-someti...