The sole benefit of Brexit would be to increase the sovereignty of the British State: the cost, which is rarely mentioned, is our loss of personal and individual freedoms and the bolstering of authoritarianism.
If we were to Brexit, the British State would have enhanced powers to control our borders, our money and our laws. Meanwhile, we as individuals, would lose the right to travel, live, work and set up businesses in the rest of the EU; the right to enjoy the benefit of all the EU laws that protect us as consumers, employees and more broadly as citizens of an EU member country; the right to have a say in how Europe develops and changes all around us including, for example, in areas like foreign, environmental and energy policy which pay little heed to national borders.
The sad fact is that Brexit would promote state authority over personal freedom.
It's the Law, Stupid: Justice: Fairness and Efficiency in Public Policy 