Buy what you can afford but when it comes to 12 volt lights I'm a cheapskate. I buy a standard spotlight bulb with the filament covered with a small pan that directs all of the light to the rear reflector. The pan over the filament eliminates the need for a hood on the light because it directs the beam forward rather than difusing it like a floodlight. I pick up a standard toggle switch at the auto parts store, a roll of black plastic electrical tape and a coat hanger with the rolled cardboard at the bottom plus about 15 ft of 120 volt lamp wire and a standard plug in for the cigarette lighter.
Take the rolled cardboard and fold it as close to the middle as possible. You'll have to trim it to a comfortable length. Wire the toggle and the bulb then wedge the toggle between the cardboard and tape it together so the toggle switch is held in place. The wire should be coming out of the bottom. Tape it well and then tape what you have to the bulb. Cut strips of the black tape and completely cover the back and the edges of the bulb. I use a low amperage bulb that won't heat up and come apart. This will not work with an aircraft landing light as they get real hot.
The result is a lightweight spotlight that will last a long time. Total cost is less than $20. If you can find a rheostat so much the better.
