Both sandwiches are pretty simple: the Chicken McGriddles places a McChicken patty between two McGriddles, while the McChicken Biscuits sees a McChicken patty between two halves of a biscuit.
Pricing varies from market to market but they're going for two for $3 here. Some locations offer the McChicken Biscuit for $1 and the Chicken McGriddles for $2.
Given that the breakfast sandwich require no new ingredients, you should be able to custom order it if they're not being offered in your area (although it might cost more).
Photo by BrandEating.com.