Generally, regular brokers only charge customers' spreads (handling fees) when trading, and charge as much as they take a fixed spread. The possible handling fee for floating price difference is not fixed.

If it is a brokerage agent, it is generally necessary to increase the commission. As you said, it may be 40 dollars per lot, or 50, 30, 20 dollars per lot, 10 dollars. This is according to the requirements of the agent. Of course, you can talk to him and see if there is any possibility of negotiation.