For those in the US, PetEdge has Greenies on sale:

Greenies

Actually PetEdge has such low prices on lots of things and also ships internationally so for those of us with currencies strong against the dollar (sterling and euro) check out their stuff; you might find things like crates are actually cheaper. They give discounts usually for buying multiples of things so if a few friends go in on buying you really save money.

PetEdge= www.petedge.com