Note, chalk is an option - and a cheap one.
I've much wondered why whiteboards became popular. Admittedly chalk can rub off on your clothes, but it doesn't stain anything, and an arbitrary piece of chalk is guaranteed to work with an arbitrary blackboard -- the same can't be said of whatever dry-erase marker you find lying around.
Personally, I just find chalk super unpleasant to use. It leaves weird dust on your hands and makes them feel all dry and weird. shudder
I don't know why anyone else likes whiteboards though.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.