Only the big whales of 10.000 BTC would be able to have an impact on the price, and even then, it would be minimum.
We saw hundred of thousands of BTC stolen from Bitfinex and we saw a flash crash and we are already recovering. The amount of money you would need is simply too damn high.
Yeah that's actually true in order to manipulate or control the price we need lots of bitcoins , but as normal people it is for sure that we won't be able to control it. There are other ways of controlling like the chinese are doing but for that we need to be famous or be a kind of person to whom thousands of people listen and follow.