BABY-SITTING FOR DOLLARS

Christina Applegate, 14, has hit the big time--a co-starring role on the ABC hour drama “Heart of the City” (it premieres Saturday at 9 p.m.)--but she’s still baby-sitting to pay for her big break.

“After her representation (agents), the Coogan Law (which protects a child actor’s earnings from unscrupulous parents or guardians) and Uncle Sam take their cut, we owe $75 a week,” said Nancy Priddy, Applegate’s mother and a working actress herself.

Mom is trying to “incorporate” her daughter to get out of the red, but she said baby-sitting keeps Christina’s feet on the ground--”She’s thrilled to get the $10!”