What's the best kind of sunless spray tan stuff to buy? How many cans would I need for one application & how long does it last?

There are a couple options on a spray on tan.  If you mean an "airbrush tan" I would look if any of your local tanning salons offer this, because it will really be more professional and cheaper in the long run!  Either way, self tanner or airbrush tan will last a week or two, just depends on the individual and how well you take care of your skin!  Quick Tan is a fine-misting spray-on self tanner that provides immediate golden color. This fast-drying, non-greasy spray provides even coverage and will not fade, streak, smear or give you an orange appearance.