I don't think the bitcoin can Easily to manipulate because if people have different thinking because otjer selling and buying their coins.
The price of the bitcoin will not become $1000 for sure this year will become more than 10,000 dollars. We know that because investors panic selling they manipulate the market last year 2018 because millions investor are panic selling .
you're right, even more so now there are so many bitcoin exchangers. besides, it requires a lot of money to manipulate the current bitcoin prices. well, we know it won't be easy even though it can. of course it is also a very big risk for people who try it.
That is why I can’t really wait for the time bitcoin price will become very stable at a very high price, let’s say like $100,000 per coin because then, it will really be too expensive for them to buy large and manipulate the market, though at this price it is now, we still have some people that are extremely rich and can afford to pump so much money into the market to manipulate it using just 1 exchange, though it is quite risky like you said, because if someone decide to buy 500,000 btc, selling it off completely might be quite difficult.
Sometimes, I feel some of these exchanges should even regulate the amount of bitcoins that can be bought at once to control some actions of these whales. But, there are having limitations only for withdrawal amounts (for their security and for other compliance reason) and bothering about those manipulations.
When bitcoin market grows and when more people are participating in "real bitcoin supply-demand" mechanism, I guess whales will lose their power to control bitcoin prices. Moreover, when bitcoin ecosystem grows in more number of adopters, there will be no more whales and even some people will be holding more number of bitcoins, they cannot manipulate against massive number of small holders.