Serena Williams has made total of $57 million in prize money in her career so far, according to the statistics by WTA. Maria Sharapova remains the second with nearly $31 million while Serena's sister Venus has made $30 million, according to data as of August 25, 2014.
Petra Kvitova, currently the Czech Republic's best player is ranked #17 earning over $15 million so far, according to WTA statistics.
Having said that, prize money is only a part of tennis players' total income. Roger Federer has made $9.3 million on court in 2013 while he is expected to have made further $45 million off court, according to Forbes, in sponsor money and endorsements