Kevin Federline is having a tough time making ends meet – despite getting $40,000 a month from ex- Britney Spears!

Even that huge amount – which comes to $480,000 a year – is not enough to fund the wannabe rapper’s over-the-top lifestyle.

"Kevin has blown through millions of dollars," revealed a source. "When he and Britney divorced, Kevin continued the superstar lifestyle, and he spends all the money that he gets."

The $2 million he received when his and Britney’s house in Malibu was sold is gone, as well as the $500,000 he received for two years of marriage. The money he earned from photos, interviews and personal appearances – estimated to be in the hundreds of thousands – has also been spent.

And despite getting a $5,000-a-month increase in child support last spring – bringing it from $15,000 to $20,000 – his spare-no-expense existence is proving to be more than his wallet can handle.

Kevin was renting a $7,500-a-month, five-bedroom home in Tarzana, Calif., that he shared with his sons, their nanny, Kevin’s girlfriend Victoria Prince, brother Chris Federline, best friend Jimmy Federico and a few part-time bodyguards.

Kevin’s food bill is more than $2,000 a month. He claims he needs to have the boys, Sean, 3, and Jayden, 2 , on a special diet because they are picky eaters and suffer from allergies. He always has a fully stocked bar with top-shelf liquors, which cost him an average of $500-$800 a month. Utilities run $1,500, the nanny’s monthly salary is $2,800, and the bodyguards get $3,000 a month, added the source.

"Kevin can’t afford the rent, his help, the food and the booze it takes to keep up the place."

He’s trying to wangle more out of Brit for the Circus Euro-tour, the insider said.