He's a millionaire, so he doesn't have to worry about spending too much
He's filthy rich so he can spend as much as he wants
He's a millionaire, so he doesn't have to worry about spending too much =彼は富豪だからお金の使いすぎの心配はないんだ
millionaire =百万長者、富豪
billionaire =億万長者、大富豪
He's filthy rich so he can spend as much as he wants =彼は相当金持ってるから好きなだけ使えるんだ
filthy rich =とてもお金持ち
少し嫉妬の加わったフレーズです。頑張ってお金持ちになった人よりかは油田王や家族代々裕福な人に向かって使います。