According to former Republican political consultant Roger Stone, The Paul Ryan Selection, Mitt Romney, in effect, sold his choice of VP to David Koch for $100 million.
As an aside, it is interesting (to me, at least) that it isn't necessary at this stage of the campaign to look to "left" sources for damaging information about Romney and Ryan. The most damaging information seems to be coming from the right....David Koch played a key role in Ryan's selection and that Koch's wife Julia had been quietly lobbying for Ryan. The selection was cemented at the July 22nd fundraiser Koch held for Romney at the former's sumptuous Hamptons estate.
Koch pledged $100 million more to C-4 and Super PAC efforts for Romney for Ryan's selection.
As Napoleon is reported to have said, "Never interfere with an enemy while he’s in the process of destroying himself."