Are you looking to make a functional searchlight, or just a prop?
The actual lights use pretty intense sources of illumination (xenon arc lamp - and just the bulbs seem pretty expensive, not including the hardware needed to power them and keep them cool enough not to explode).
If it's simply a prop you want, to accentuate the look of your haunt, you could probably make one with a halogen shop lamp as the light source - perhaps cut a plastic water barrel in half, line the inside with mirrored window film, and put together a framework to hold the lamp away from the sides, pointing in, so the light is reflected out.