Assuming acrylic to allow easy drilling, if not store bought glass tanks quite cheap (and could be drilled).
Check out Scavenger home built tank in the this post (I'm impressed):
http://www.canreef.com/phpBB2/viewtopic.php?t=18899
Could make a plywood box with the non-viewable sides lined with thin acrylic sheet, in the front, thicker piece for the viewing pane.