Brian Diaz , May 26, 2004; 05:46 p.m.
Foam core is a great, cheap reflector. It's essentially 2 pieces of posterboard sandwiching a piece of foam for rigidity. It's often found in office and art supply stores. Tape some aluminum foil to it, and you have a silver reflector.
For more portable options, I've used silver collapsable windshield screens from an auto parts store. It's like if Photoflex sold their Lite Discs 2 for $10, rather than $50 each.