$150? Perhaps for some of the serious mods, or a very large supply, but most of the starter kits shouldn't be close to that high.
The mall kiosk costs about $40 for a kit and they take cash. I'm not even sure whether they check ID; they probably should, but whether they'd actually stop a kid? I don't know, though I doubt it for some of those guys at least.
On the other hand, kids are quite internet savvy now. You can buy a prepaid credit card (Visa, Mastercard, etc) at almost any gas station, or Walmart. You can use those to pay through paypal or many other online payment systems, and none of them really have any way to validate your age - there's no ID check, no chance of someone ratting you out. It's not more expensive, I think we've already paid less for the ecig supplies than analogs after about 6 weeks.
I don't know that it really is converting kids, but then again I'm not sure why so many new kids pick up analogs now and I could see the electronic ones as seeming more attractive than those at least.