Some surprisingly straight campaign talk from The Associated Press:

Republican John McCain is making promises that would cost billions of taxpayer dollars, yet he is vague about how he would pay for them. [...]

McCain has pledged to balance the federal budget, although he has backed off an earlier promise to do so in his first term and now says he would do it within eight years. [...]

[He] proposed a new mortgage refinancing program for struggling homeowners that could cost the government $3 billion to $10 billion. He proposed to suspend federal gas taxes for the summer months at a cost of $8 billion to $10 billion.

And McCain has several proposals whose costs are unknown, such as his pledge to give all veterans a plastic card to get medical treatment anywhere they choose, a new student loan program and tax write-offs for companies that provide Internet service to rural areas.

How would he pay for it? New user fees could pay for the gas-tax holiday, McCain adviser Doug Holtz-Eakin said. [...]

[F]or all the numbers he has provided, McCain has been reluctant to say exactly which programs he would cut.

Whole thing, with plenty more details, here. I might also add that trillion-dollar wars tend to be expensive, as do plans to boost the standing military by 150,000 troops, etc.

It is perhaps noteworthy to point out that this is almost precisely the opposite of John McCain's tax/budget philosophy of 2000, when he was a big (and convincing!) budget hawk and debt-payer-downer. Here he is in his 2002 memoir Worth the Fighting For, talking about his differences with George W. Bush on that score:

He and I disagreed on tax policy. My position invited greater hostility from conservatives in the party and in the press than my support for campaign finance ever had. Republican primaries had long featured a bidding war to see which candidate could promise the biggest tax cut. I chose to offer the smallest, targeted to middle- and lower-income families, so that we could use most of the budget surplus to pay off the national debt, build our defenses, and begin to pay the transition costs of reforming Social Security and Medicare for the sake of future American generations.

Lest anyone think my positions were brave, if self-defeating, honesty obliges me to note that every poll my campaign conducted (and we took as many as we could afford) found greater support for paying down the debt than cutting taxes for upper-bracket incomes, among Republican voters as well as Democrats and independents. [...] You will have to trust me that I held and expressed these views before I had survey research proving their popularity.

Readers of this website might also find of interest the selection immediately preceding the passage above:

I welcomed a greater, if still limited, role for government in national problems, anathema to the "leave us alone" libertarian philosophy that dominated Republican debates in the 1990s. So did George W. Bush, I must add, who challenged libertarian orthodoxy with his appeal for a "compassionate conservatism." He based much of his more activist government philosophy in an expanded role for the federal government in education policy and in his support for contributions that small, faith-based organizations could make to the solution of social problems. I gave more attention to national service and to a bigger role for government as a restraining force on selfish interests that undermined national unity. But his positions did him much credit, as well they should have, and they do him much credit now as he uses his presidency to advance them.