Here is a DIY just the way we like it: 3 uses in one, easy to build, light weight and dirt cheap.
Tiffany Angeles shares a nice DIY she uses in her photography studio. It is a huge 4×8 reflector made from a 4×8 polystyrene insulation sheet. This is probably the biggest easy-off reflector you can find.
Those boards can be found in the sheet insulation section of any local hardware store and are perfect to work with as they are so light and easily pierced.
The DIY talks about painting one side of the sheet to use it as a reflector and using the other side as a background. but I would probably paint one side black and use it as a flag or a gobo similar to this one used by Matt Haines.
While the boards are not free standing out of the box off the shelf Tiffany shares a quick way of using shelf brackets screwed on the bottom as supporting legs.
Total cost: around $30 per units. Pretty awesome if you ask me.