It is free to use cTrader trading platform. Also opening a Demo account and trading on it, is free.
There is no fee or cost charged against Demo account users.
You can open a Demo cTrader account directly from the trading platform or from the official websites of cTrader brokers.
In case of live trading accounts, you may need to make a deposit of your funds. Then there are certain risks and fee involved while trading.
The trading cost on cTrader trading platform is different by each broker.