Anyone who has looked at the radiant barriers at the home stores has probably gotten sticker shock. the best places to use this stuff as far as best bang for the buck goes is as a water heater wrap and in the garage door. Enough from the home store to do those places would be quite high at my local price of about $20 for a 16" X 25' roll.
The other day, though, I found this place:
Radiant Barrier Reflective Foil Insulation, Energy Efficient Products and Information.
They have a garage door kit for $85 for a double door. They also have a water heater wrap kit for $30. I ordered both. I'll post later when I get them. their bulk material also seems to be a good price.