There is this stuff I discovered not long ago called blackboard paint.
The idea is going here because I think I could actually make stuff like this to sell
The paint is not particularly expensive, and can be got at a hardware store. As well there is a base coat you can get that will add metal to the base for something that you can stick magnets to. I will update this if I get to the magnet paint, because I suspect it would be very weak.
The primary idea I am holding is to get some frames from the thrift store and paint the glass.