Who’s she running against? If it’s Sarah Palin, she could do it on a shoestring.
Seriously? Your time-table is too aggressive. She’d have to build up some kind of credibility first – governor of a state or a term or two in Congress. That takes years as well as money.
If you wanted to do it by 2020, you’d have to resort to actually bribing the electorate, which is not only illegal, but would be prohibitively expensive. Let’s assume it was legal. It would still be economically disastrous, as that amount of cash flooding the system would lead to inflation. Sure, for a few million dollars, I’d probably vote for her (because I could always move to Tahiti if things went to hell locally), but everyone else would also be millionaires. If you want them to go to work in the morning, you have to raise prices on everything.
You might argue that the price of some people’s vote would be considerably lower and it’s true that some would vote for her just out of amusement. And history does show that some people will vote for any pretty person with loose enough morals. But realistically, she won’t get the Republican vote because, hey, sex tape. And she won’t get the Democratic nod because no party likes to be a world-wide laughingstock.
So, really, the only plausible scenario is one in which aliens land and offer the secrets of immortality and free energy in exchange for electing Kim President. So … how much does a radio telescope and a broadcast tower cost?