[Shop-talk] Cheap, strong, flat file storage?

[Jim Franklin]

An artist friend needs a way to store a lot of flat paper material but on many different shelves; essentially a drafting storage unit but at an artist's price. Safco has stackable plastic units similar to desktop units that hold 8.5x11 paper, but they're 42 x 30 or so. Problem is they cost about $60 per tray. Used drafting storage units are still many $100s. 

We're trying to come up with a thin, strong material that can be slid into slots in a frame, kind of like baking sheets on a rolling cart. The frame needs to roll and be strong enough not to rack when moved. 

I've made bookshelves and entertainment centers with 3/4 melamine and threaded rod, but that's heavy and wobbly.  Even 1/4 plywood tends to buckle and needs to have a finished edge. 

Any ideas on what to use or repurpose? 

thanks,
jim