Home Depot or Lowes sells large 8′ by 4′ panels of what they call hardboard paneling. This is very inexpensive at just over $13 a sheet. Oddly enough the surface works just great as a white board. Compare this to a white board of the same size which is around $300.
If you clean the surface with a regular cleaner like Windex or 409 it will strip the surface and you’ve got a permanent marker board. But if that happens just go buy another replacement panel.
This stuff is also light enough you can hang it on a wall with double sided tape. Be careful with a painted wall as you can peel the paint off when you pull the panel off the wall. I’ve also mounted these panels with molly bolts.
When I worked at Online Software they had classrooms with the entire front of the classroom paneled with white board. I copied that idea but used this less expensive paneling. We paneled an entire conference room at The Price Club by putting the panels on the wall standing up. We had to cut down some panels to fill the entire wall of the conference room. Have a pile of markers and dry erasers on the conference room table. Anyone can stand up, turn around and start diagramming on a floor to ceiling (8′) white board. Very cool.
Nimble Union 
Showerboard is similarly available and priced, and erases rather nicely without other cleaners.
I think this is Showerboard but these home improvement web sites don’t call it that.
So if you don’t use cleaners like Windex or 409, what do you use to clean it?
What do you clean it with?
Use a soft cloth in general and standard white board cleaner liquid once in a while.