Running around in a bikini seems to have paid off for Kelly Bensimon. After the former “Real Housewife” was photographed showing off her beach bod in Miami this month, she e-mailed friends yesterday, sources say, announcing a new modeling contract. Under the subject line, “I’m modeling again,” Bensimon says there will be a party tomorrow to “celebrate my new representation.” Bensimon, who’s also a jewelry designer and author, began her career as a model.