Patrizia D'Addario, a model at the centre of the latest claims, said she was paid $1,386 to attend a dinner at Berlusconi's Rome residence, along with a number of other young women, in what she described as a "harem".
She told an Italian newspaper she returned a few weeks later to spend the night with the prime minister, and that she had tapes to prove it.
Another woman who accompanied the model to Berlusconi's residence told newspapers that D'Addario said she slept with the premier, but had not asked for money because she was more keen on favours to obtain building permits.
The second woman has also said Berlusconi presented her with rings and necklaces he designed himself, as well as cash.
But Berlusconi, who is coming under increasing political pressure over the scandals, said D'Addario was "very well paid" to make the allegations, prompting an investigation into a local businessman who is accused of recruiting and paying the woman.
The opposition and the influential Catholic Church have demanded the prime minister clear up the facts.
The latest scandal comes after Berlusconi denied having sex with an 18-year-old, and accusations from his wife that he "frequents minors".
The prime minister has accused the media of mounting a smear campaign before the G8 summit, which he is hosting next month.