I once made a white board out of one of those transparent office chair mats. I just stapled it to my white wall. I never ended up using it extensively, but it worked pretty well. If you want them professional-looking at more cost and slightly more work, consider just painting the back of a piece of plexi glass white, or just the wall behind it. That's how this institution solved the same problem

(Edit: I researched some more and, due to ghosting issues, acrylic glass (or plexiglass) is not an ideal whiteboard material.) You could make 10 giant white boards for ~1000dollars, according to this website. A cheaper, if less stylish option, buy these 4'x4' panels for ~50 each.

If you want to go even more DIY, here's a list of whiteboard materials:

1. Melamine

2. Painted steel

3. Ceramic (glass) fired onto a steel surface in a kiln. The only material which does not ghost if the ink is left on for long periods of time.

4. PET, Polyethylene terephthalate-on-steel

http://en.wikipedia.org/wiki/Whiteboard#Surface_materials.

Melamine seems like the best bet. Look for melamine-laminated plywood, as it will likely be as high-quality as most store-bought boards. Here's the type of thing you'd want, and it's very cheap. But you'd have to find someone willing to sell it in small quantities.

Note, chalk is an option - and a cheap one. This chalkboard contact paper is very cheap and has excellent reviews:http://goo.gl/samVWk What's that you say? You're too cool for chalkboards? I assure you, you're not. If you do decide to buy the chalk paper, remember it must be applied to a smooth surface - one reviewer recommends masonite board. You cannot stick it directly to a wall, unless the wall is abnormally smooth. Same goes for spray-on chalkboard coating - which works very well, too.