He must buy his wife a lot of crap
I mean, how do you pitch that one? "So yeah, honey, today I'm gonna start on my badass batcave. And, oh yeah, I gotta have sliding bookshelf access and a crazy awesome tunnel after that. I'm pretty much just gonna spend ridiculous amounts of money because I can, and.. well.. you don't make any. So you're gonna sit there and smile throughout the entire undertaking."
Sounds good to me