On Bitfinex i think are the lowest fees 0.15% per buying and selling.
and if u wanna trade a lill bit more risky, you can choose to margin trade where a leverage is 2.5:1.
I don't trust these opaque exchanges! I pay an outrageous 2% plus spread to Coinbase for every sell/buyback and I can't even do a simple f#cking limit order. Second Market wants to play New York Bitcoin Exchange and they don't have a single goddam broker I can use. Kraken needs to get crackin' if they want to be the Charles Schwabb of BTC.
I'm a buyer at $645 and a seller over $695 until the weekend or until the next breakout, whichever comes first.