how many do you want to order at once?
Shipping can kill you, but even hobby lobby stocks some and you can use coupons.
The nearest hobby lobby is 6 hours away :( shipping is the killer.. I want to have at least 10 of all sizes on hand.
^^^^ The boxshop above is recommended by most and very flexible to stock the supply you are looking for. In large quantities of 1000+ I think there are a few cheaper sources.
Do you have a cash and carry place near you? I know by me, I can buy from a cash and carry place for very cheap! A box of 200 single cupcake holders for 28 bucks :) or a dozen holders, 100 of them for 61 bucks. Otherwise, the boxshop is also a good site to use!