Subprime lenders posted strong earnings during the third quarter. But while profits are up, so, apparently, are the costs of doing business. A case in point is New Century Financial, which reported $51.5 million in third-quarter net income, up from $16.7 million during the same period last year. That strong performance boosted the company’s nine-month earnings to $125.4 million, an increase from $24.8 million in 2001. Total revenues