Not sure if anyone will ever follow-up on this answer, but I stumbled across it and had to make a couple corrections. Jomifl, while you are correct in saying that 1000W should equal 1000W for any appliance theoretically, you forget about the basic efficiency of appliances and efficiency of different energy transfer. The crux of the matter here is that whilst conventional electric ovens transfer electrical energy into heat by passing current over a heating element, a halogen oven produces much of its heat as light, in the form of IR waves. Conventional ovens and heating elements are very efficient at heating by conduction (hence the rapid-boil of a kettle), but do not transfer as effectively over distances (i.e, the space inside the oven). This, along with the inherent time needed to bring the element to temperature, results in a relatively slow warming up rate, resulting in wasted energy. The halogen oven, by comparison, reaches its maximum temperature relatively quickly. While the amount of power given to it may be the same, the heating element and method of transfer (both convection and transfer by IR waves) are much more efficient than convection alone. For a good analogy, an energy-saving bulb can emit more light than an incandescent bulb of equal wattage. The quicker rate of warming and more efficient method of transferring energy (by waves instead of convection) means that a halogen oven will always be more efficient at cooking food than a conventional oven of equal rating. This effect is made more obvious when we consider that a halogen oven typically cooks food faster than a conventional oven, even though its power ratings are typically lower.
To conclude, halogen ovens are cheaper to run than conventional ovens.