Two words: Mun. Knee.
No matter how you slice it, the only Republican with either the personal resources (Mitt Romney) or access to donor lists (errrrrrrrrrr, no one?) to raise enough money to make a serious run at a candidate with a billion dollar war chest is, um, Mitt.
And he ran already. And lost. And spent an awful lot of his fortune doing it. If I was his kids, I'd be pretty pissed right now.