The blades are a big problem, as they must be thin with straight edges.
I found a custom window blind maker who would sell me some black aluminium window blind material. It was very cheap, if a little narrow. Before being made into a window blind, this material is unperforated and flat, so it works well when pinned to a steel sheet by fridge magnets (or simply weighted down).
If you can find it, the material is sold by the meter off a roll, so you are not limited to any particular length.
I used this material as a temporary mask, but I guess it could be built into an easel with a little ingenuity.