Even with Bitmex had no fee i do still have some doubts on using it. I was shocked when i saw the volume trade for the last 24 hours which is currently on rank 2 on all  exchange when it comes to volume.
Due to that 100x leverage which do give out some interest- Just  a presumption though. As omegastarscream given about on those links you can search up for those exchange who do have zero fee but same as advised on the dude above never do easily entrust too much.