Billionaire Mayor Michael Bloomberg (search) has poured $46.6 million of his own cash into his campaign for a second term, including nearly $20 million on advertising, according to finance reports.

The media mogul with a $5 billion fortune, which makes him the 40th richest American on Forbes (search) magazine's list this year, spent $74 million on his first run for mayor — equal to about $100 per vote.

With the election less than five weeks away, he is on track to break that record spending spree: In 2001 at this time, he had spent about $29 million.

Democrat Fernando Ferrer (search), who has burned through a total of $6.6 million — about half on advertising — said the Republican mayor's spending is "distasteful" and "obscene."

Bloomberg said he needed to spend millions in 2001 to educate voters about who he was and what he stood for. This year, he has argued that his millions are helping inform New Yorkers about his record in office.

Bloomberg's campaign spokesman, Stu Loeser, said Friday that the mayor's riches also enable him to govern with no special-interest strings attached.

"New Yorkers know that Mike Bloomberg is beholden to nobody but them," he said.

Ferrer, a former Bronx borough president, is running against Bloomberg's bottomless bankroll with donations that average $416. He has just $556,000 in the bank now, and is counting on $315,000 in public matching funds next week. In the latest opinion poll he was trailing the mayor by 15 points.

Bloomberg's $20 million television and radio advertising blitz began in May with a television spot in Spanish. Since then, the campaign has bombarded the channels with ad after ad — so many that the campaign refuses to disclose the total number. The spots mostly tout the mayor's first term accomplishments like lower crime and better school test scores.

On the night of the Sept. 13 primary — when Bloomberg wasn't even running on any ticket because he faced no primary challenger — the campaign spent $50,000 to take over the Brooklyn Marriott (search) with a huge bash that featured a live band.

The tightly-controlled campaign also has a costly daily operation. Rent for their seven campaign offices, plus the sleek 19th-floor headquarters in Times Square (search), has cost them $745,888 so far.

Wages for campaign workers — who are plied with tasty takeout, coffee and other treats worth thousands of dollars — total more than $1.9 million to date.