Yes! What Armorist said!
I bought a "Cavelier Hat" last year at one of those Halloween Superstores for $12. One side was already pulled up and attached with velcro. I simply pulled up two more sides, stapled them in place and - voila! - instant tricorn. It even came with a red feather but I replaced that with a couple of dyed ostrich feathers.
It's not perfect or historically accurate, but it is cheap.