At the moment it isn't feasible because current screens on the market aren't able to be flexible enough. Hopefully however there will be some new technologies advancing the backplane design because it is this which needs to be mounted on some support meaning the screen isn;t flexible. The frontplane should be flexible though.
I would imagine something like a bag would be first and clothing sometime after - I imagine that it might be a bit uncomfortable in clothing entirely made from e-paper as it won't "breathe" but patches could certainly be done.
Costwise you'd expect them to be expensive at the moment, but hopefully as more companies come to the market the price will be driven down.
If you haven't seen it, there is one fashion item which you can buy at the moment - there is a watch with an e-ink screen.