You can buy halogen worklights quite cheaply at a hardware store. I bought a two-fixture light (500W x 2) on a stand for $35. These are floodlights with a broad illumination pattern, and if you want to restrict the light with "barndoor" flaps such as are found on professional lighting equipment, you have to make your own. This page describes one way to do it. I advise you read the entire page first before trying this yourself. Note, the bulb and reflector of the worklight form an extended source, so the shadows cast by the flaps will be fairly soft. You'll never see the hard-edged beam you would get from a fresnel type instrument. If you want an even softer light, try a "painter's light" such as the Regent-Cooper PHL300 which is a 300W halogen worklight with a diffusing glass face, plus a special "color-corrected" bulb for more accurate color, see also my accessories page.

Construction:
I formed a square wire frame around the light using 1/8" diameter brass rod. Be careful to make the frame larger than the window face of the light; otherwise light will leak outside the edges of your barn-door flaps when you are done (the wire framing in the picture is a bit too small as you will see). The particular lights I own have a "shoulder" profile which enables me to simply hook the wire over the front bezel on each side for support. In this way the barn doors are easily removed, and no fasteners are required to hold them on. Make the frame with two pieces of wire; the main one a U shape with the hooks on each end as shown; the other piece a straight rod going across the top and soldered on each end. I used silver-bearing solder (stronger than standard tin-lead type), flux and a propane torch. You may find the end-on butt joint shown below to be too weak; a stronger joint would have the cross wire curl around the vertical member for support.
 

I spray-painted both sides of the steel sheet with flat black paint before cutting it with the tinsnips. I ended up needing two sheets for the flap size I wanted, and I tried two different kinds of paint as shown in the photograph at the top of the page: a normal flat black primer from Krylon, and a high-temperature barbeque grille paint supposedly good to 650 degrees C (1200 F, which is a glowing red heat). In practice there seems to be little difference; both paints will start to smoke if you use them to block off a lot of the 500W light, although their temperature is still far below 650 C. Perhaps the smoke will stop if you bake them long enough. I think "pro" barndoors have black oxide or anodized finish which is more heat resistant.

Before cutting I made some test patterns out of construction paper to get the size and shape correct to fit the light properly. The side flaps are the same size as the width of the light so they can both fold over it all the way. Be careful to leave a "tab" of material on the edge which can be curled around the wire as a hinge. Watch out for the sharp edges of cut sheetmetal also. If you have access to a sheetmetal shear (most machine shops have them) you can get much cleaner and straighter edges.

If I were to do it again I might make the flaps even longer, giving you more directivity, although that way they could not fold up flat for storage or transport. After cutting out the flaps I curled them around the wire frame with pliers as shown above. Crimping the metal tightly around the brass wire gives enough stiffness to the joint so that the flaps stay where you put them.

As you can see in the pictures below of the finished light, the wire frame is not quite large enough on one side for the doors to completely prevent light leaks (left image). If you make the frame large enough you can prevent this (image second from left).
 

This construction project does give you an alternative to professional video lights on stands. It is cheaper than the store-bought type, but of course more work for you. Note, since the typical 500W worklight fixture uses a long horizontal bulb, the barndoors do not give as sharp a falloff in the light horizontally, as they would with a more compact bulb which is closer to a point light source. Also, if you have the doors nearly closed off for any period of time, you will get a bit of smoke from the paint, so ensure adequate ventilation.