Yes Bittrex is the only one trading SBD and STEEM. The transfer to Steem Wallet costs only 0.01 but you first have to change the bytes to BTC and then the BTC to SBD or Steem. And that costs a little money. But it's not very much.
Here the link for the one who wants to change it himself, I know that some don't get along and the course can change within minutes. https://bittrex.com