Just buy some plexy glass, make a frame and use that. You can probably buy it at a hardware store or home improvement store. Or perhaps try to find a glass topped table at a tag sale or something and buy it cheap. Take the glass from that, make a frame, and there you go. Perhaps even look at one of those second hand/overstocked places that sells building materials for cheep for glass or a window. I dunno, be creative.
Visa-Vis pens I believe are the kind that teachers use on overhead projectors (haha remember those). They are like dry-erase markers but they don't erase without water and they come in like 200 different colors.