I found what looks like a very good Trading Volume chart at
data.bitcoinity.org
That is a very bad chart. It doesn't show the depth of the market, and that is what you wanted to know. Also, the Chinese exchanges with their "no commission" bullshit are obviously way higher in volume than the real exchanges. Generally speaking you have to check the biggest exchanges one by one with their order books to get an idea how much money it would take to move the price by X...
For market depth check this out:
https://bitcoinwisdom.com/markets/bitfinex/btcusd