You’re a Republican, but the top candidates in your party’s 2008 Presidential sweepstakes, Senator McCain and Mayor Giuliani, are not your cup of tea. Or you’re a member of the donkey brigade and take a dim view of such leading contenders as Senators Clinton and Obama.

So with the general election now just 22 months away, you boldly decide you’re going to give the front-runners a run for their money by seeking the presidency on your own. Lo and behold, miracle of miracles, you sweep through the primaries and snare the nomination of one of the two major political parties.

Sounds terrific, except to pull off this incredible upset and win the general election be prepared to shell out huge bucks because “the economics of running for president are almost getting out of hand,” the Center for Responsive Politics says.

The Center figures that the next occupant of the White House will have to spend about $500 million to grab the nomination and win the general election, an all-time high, its communications director, Massie Ritsch, tells me.

In the 2004 election, President Bush spent $367 million on the primaries and the general election, while John Kerry anted up $328 million. In contrast, Ralph Nader raised only $4.5 million for the contest.

A professor of politics at the University of Virginia, Larry Sabato, reckons a $500 million price tag to make it to the White House is just about right. He estimates about 80%, or $400 million, will be expended on press advertising, notably for TV, radio and newspapers. The rest: largely for consultant fees, travel, and staff.

One thing is certain. It helps to be a billionaire, like Mayor Bloomberg — who may or may not be a candidate — if you’re out for the nation’s highest office, since you can spend as much money as you would like to win both the nomination and the election. However, under such circumstances, you cannot take government (or taxpayer) money, which, though not specifically defined at the moment, is slightly more than $80 million for the major parties’ candidates, according to the Federal Election Commission.

Individual contributions are limited to $2,300 for the primary and a similar amount for the general election.

If $500 million is too rich a price for your political cravings, you might want to lower your political ambitions because the costs associated with less exotic political positions are considerably lower.

Mr. Ritsch notes, for example, that in the 2006 election cycle, depending on the locale, the average amount of money raised for a senatorial race was $3.3 million, although to win it actually took an average $7.8 million. Some, though, using their own money, have spent a lot more. For example, it cost Governor Corzine of New Jersey, a millionaire, $63 million to win a Senate seat in 2000.

To win a seat in the House in the last election, the average cost was a mere $1 million.

Speaking of how being a billionaire can help ease the way for a White House run, speculation continues as to whether Mr. Bloomberg (estimated net worth: $5 billion) might toss his hat into the presidential ring.

One of his longtime close friends in the financial arena tells me his latest sense of it is that the mayor, who has been quick to belittle presidential speculation, very much wants the job, but is still undecided whether to go for it. “If he does take the shot,” the mayor’s friend says, “I think it will be a very last-minute decision after he assesses what’s happening on the political front.”

His predecessor, Mr. Giuliani, could have much tougher financial going. Mr. Giuliani hasn’t officially declared yet for the presidency, but according to published reports, he has set up a fund-raising goal by March of at least $25 million. “Not enough if he’s intent on being a serious candidate,” says the Center for Responsive Politics. “He’s still got another $475 million to go.”

dandordan@aol.com