Tax cuts don't "cost" jack shit, unless you presume all incomes belong to the treasury.
Actually they do - and if you check with almost any media source which covered the story, they will tell you the same thing.
Tax cuts cost money because they mean the government earns less. When governments earn less, they borrow.
Borrowing money costs rather a lot.
Given the US already runs staggering deficits, Romney's plan to increase thos deficits by a further $5 trillion leaves a hole in the government coffers the size of the Grand Canyon.
While his much touted closing of tax loop holes - but so far unspecified - will bring in some money, your net situation will almost certainly be worse than it is now.
Cutting expenditure will help, but the extent of the cuts needed to cover the deficit the US has now are political suicide - and Romney wants to add another $5 trillion to that.