The fees at OKEX are probably the lowest in the industry, at the time of writing of this review. There is a 0.03% fee for opening a new position and nothing is charged for the closing transaction. This is a lot better than the average of around 0.20-0.25%, offered by most other exchanges. On the other hand, the forex brokers, who provide Bitcoin trading include their costs only in the spread. While it is a bit hard to compare spreads and commissions based on size, you can check out this post to get a better picture.