It doesn't need to be "funded". Government spending creates money and taxes destroy it. The role of taxation is to drive demand for currency, and drain money out of the economy. It can also be used to disincentivise behaviour. But tax cuts don't need to be "funded", because governments have no issue with affordability -- they issue the currency.

Video on how this works: https://www.youtube.com/watch?v=i35uBVeNp6c

Book on how this works: http://www.amazon.com/Modern-Money-Theory-Macroeconomics-Sov...