There isn't a magic number and it varies among people of different athletic ability, but don't skip them. "A lot of people make the big mistake of learning just a teeny bit, then getting straight on a pair of skis," says Jay Peak's Kennison. Basic techniques like turning and wedging, along with how to transition from flat to steeper terrain, are skills that probably won't be picked up with just a single lesson, he added.
Additionally, many ski resorts offer beginner packages that include lessons, rentals, and lift tickets designed to cut costs. Do some research and find the best package that might work for you.