GlutenFree Mall - http://www.glutenfreemall.com/ or http://www.breadbeckers.com/buckets_bags.htm#QUINOA, both have 25 lbs for less than $40. The Mall also has 12 oz boxes. If you are looking to buy from the producer, try http://www.greenearthfarm.com/quinoa.html
Here is a link that might be useful: Glutenfree Mall