Nobody knows whether Bitfinex is insolvent or not. As a result, dollars at Bitfinex are worth less than dollars at other exchanges. This accounts for the price difference you see. To exploit this difference, you would have to send dollars to Bitfinex and command them to make what appear to be fraudulent transfers on your behalf.
See this article for more details. Some excerpts:
Bitfinex has imposed a haircut on all of their depositors.
For those whose deposits were not held in segregated accounts, there is no question that the deposits constituted general obligations, payable on demand, on the part of Bitfinex. To justify making anything less than a full payment on a general obligation that is payable on demand, a company would have to be insolvent or illiquid.
By definition, if you don't have sufficient assets to make the payments you are obligated to make, you are insolvent. There's no reason to think Bitfinex has assets that are not liquid. They imposed a haircut because they don't have assets to cover the funds their depositors have every right to demand from them. They are insolvent.
When you deposit funds at Bitfinex, they have your funds. You have a promise that they will repay you the funds you deposited. But you're just another creditor on their list of creditors. You get funds if they have them and not if they don't. Your deposit is another general obligation of Bitfinex, a company that is insolvent.
An insolvent company cannot make full payment to a junior creditor without court approval (or consent of all their creditors) -- such a transfer would be fraudulent. We know Bitfinex has not gone to court as they would have to have given notice. When you deposit money at Bitfinex, you become a junior creditor. When you command a trade or withdrawal, you are commanding full repayment of yourself, that is, you are ordering them to make a fraudulent transfer on your behalf.
Fraudulent transfers are subject to clawback. That is, if you trade at Bitfinex, you may eventually get a letter from a trustee or receiver demanding you repay the money you made or even the full value of the assets you withdrew.
