Hi! Thank you for research!
http://Changelly.com takes a reasonable 0.5% fee for each exchange. Plus regular blockchain withdraw transaction fee, here is 0.0002 BTC.
It seems, that other similar exchanges, doesn't consider withdraw commission. That's why better to compare rates for higher volumes. For example one of our users, Hive account@fav make a calculation for 10 STEEM, and Changelly shows best exchange rate: https://steemit.com/steem/@fav/let-s-check-the-fees-converting-steem-to-bitcoin-asap