For vitamins, the quantities on the site reflect what's included in a daily pack, and prices on the product pages are the price per month! So for example, Vitamin D is $5 per month, and you'll take one pill per day. You'll get a box with 30 daily packs. That means your cost for Vitamin D is $5/month or about $0.16/day.
Powders work a little bit differently. Since they're not necessarily meant to be taken daily (though you're certainly welcome to do so!), the quantities reflect what's included per month. Ordering a five-pack Chill Factor, for instance, will get you you 5 sticks of Chill Factor for $5 that you can use as-needed throughout the month.