Kaya's gotta be worth at least 6.
In all seriousness, I believe a lot of bandmen actually do have side jobs and their music career is not their real one. That's why a lot of ex-Matina guys who are now "retired" now have regular desk jobs or why some of them own bars / host clubs. I think unless you are in a band with a fairly intense touring schedule that sells well, you'd need a side gig, such as hosting or modeling, to keep afloat. A lot of bands also post their tour schedules for the upcoming 6 months, but if you look, it's usually like 4 - 7 gigs a month, which I'm assuming is no where near enough to feel financially secure.
Groups signed with big indie labels, such Shimizuya, PSC, -AINS-, Goemon, and BP Records, are probably fine with just making music, but would need to find something else once their current band splits. Very few people are like Yoshiki with race cars and pianos made out of smaller pianos