I usually buy from
Carpe Diem Store: Art, Architecture, Hobby and Crafting Supplies, But their shipping is expensive if you are not buying a big lot. The prices are actually cheaper then what is shown, once you put the item in your cart you will see the correct price.
I also noticed markerpop is competitive as well. Good Luck, I normally buy a couple at a time and use my Michaels coupon for the ones they have in stock.