Generally the landing lights run on 28 Volts a.c. and, although most are around 800 Watts, can run up to 1.5 KW. We are seeing some 6.2 Volt quartz halogens these days.
Expect to pay US$250 and upwards for an ordinary sealed beam unit with an airworthiness tag. That's just the lamp, mountings and fittings are extra.
One of our technicians at Brize Norton rigged a VC10 nose taxi light in the rear window of his Cortina. He used it to persuade following cars to dip their headlights...