I also use coinmarketcap to know the coin price, it is just a benchmark and can not be used as a reference. The actual price is the price that is on Exchange.
IYE, I also use the coin market cap, but I did not make reference to know the price of the coin. I use coinmarketcap.com as a reference to suply coin. because, as you say, the price is actually existing in the exchage/market.