Ok, so this is my entry into the hack It Challenge. Here, we're going to use two separate lights to make one awesome headlamp!. Let me first stipulate that $3 depends on you materials cost, it may be higher or lower, but either way you get a decent lamp out of it.
Disclaimer: A soldering iron is used in this instructable, barely, but its a good idea to know what you're doing with one.
Step 1: Materials and tools
First, source your parts. I got a 9 LED flashlight for a dollar as well as an incandesant headlamp for two dollars from HF.
Short length of wire
small phillips head screwdriver
pair of pliers/vicegrips
Step 2: Disassemble Lights
Disassemble the Flashlight and headlamp. In the case of these specific ones, the headlamp came apart by removing two screws that were accessible when you unscrew the lens and reflector. The Flashlight required a little brute force to free the required parts, but i'm sure that some patience would help you save some cool parts.
Step 3: Modify LED array
Now we modify the LED array to be accepted into the Headlamp fixture. First, bend the contact spring located on the back perpendicular to the array. You're essentially making a spade connector. Next, solder a lead onto one of the negative contacts on the LED array. This particular one has 4 points built in to ground it to the case, so i just used one of those.
Step 4: Attach LED array
Attaching the LED array is as simple as connecting the wire, plugging in the array, and screwing on the lens. To get the wire into the connector, i used a small flat head screwdriver, the friction force is more than enough to maintain a good electrical connection.. The Bent spring, acting as a spade connector, plugs into the other connector. Do a quick check to see if it lights up, if not, try flipping your connections. The LED array hangs free by the spring until you screw the lens (minus the reflector) back onto the headlamp. Tighten until it is snug, and all the parts inside are now secure.