I'm asking this because I still don't really know enough about market capitalization as a source of valuation. A company's market cap is determined by the last transacted price, so theoretically you don't really need a billion dollars of cash to make a billion dollar company.

That said, how would this mechanism work in a pump a dump? Do you need 100m of cash to increase a company's market cap by 100m? When you dump your shares, do you profit as much as the loss of other traders who bought in after your pump or could they lose even more than that, resulting in a dead-weight loss for the market? (Or if they lose less than that, a net gain for the market).