David Engler had been pretty sure he didn’t want children. Then a frustrating school day two years ago helped seal the deal for the now 43-year-old substitute teacher. “It was wild. I had to call the office seven times to get kids pulled out,” he said. “The next day, I called Kaiser and said, ‘I’d like to know how much a vasectomy is.’” A representative with Engler’s insurer, Kaiser Permanente, told him the procedure would be free because it was a form of birth control, he said. But after undergoing the vasectomy last winter, he received a bill for $1,080. “I felt defeated, tricked, and frustr…