I just got report covers at Office Max, I believe. They weren't expensive at all. Maybe like $4 for 8 of the actual covers, then the crafting mesh I got at Walmart for $1.97 and that came with like 5 or 6 large sheets so I have plenty to make more. You can probably get the report covers at Walmart too.
These are what they look like and the plastic part just slides right off.
EDIT: Oh and the plastic mesh gives enough force that you can squeeze them in there and the tension holds them in place. The mesh may bow, I just kept trimming a little at a time to where it still is snug against the glass but doesn't bow.