Financial transaction tax probably.
Actually, I would cut off all other social expenses like unemployment insurance, pension, etc. (with the exception health insurance) and replace it with the UBI. This will also save some administration costs.
Also reducing poverty and increasing the whole national income is one of the smartest investments you can make. Consumption will skyrocket and thus the national economy will prosper. Think of the other positive effects that poverty reduction has like falling crime rates.
Since the UBI is proposed as the answer to automation, we still have our economic productivity provided by the machines. But who shall receive the value created by robots? Only the machine owners or should all people benefit from it in the same way?
There are also some statistics from the US showing that although the overall productivity level has grown over the years, the worker's compensation didn't. So we're creating more value without getting the adequate money for it. UBI is a matter of justice to fix that.
And finally the costs of a UBI turn out to be way lower in the end because at the moment we're often just looking at the gross price tag instead of the net transfer amout. This guy did the math and the whole cost thing turns out too be way less scarier than expected.
RE: Is Universal Basic Income the Answer to Automation?