Generally, plastic landscape lights are cheapest, metal are more expensive, and solar are the most expensive. Also, getting complete kits (including lights, cable, and transformer) is a lot cheaper than buying the parts piecemeal.

Another consideration is light bulb power. Standard low-voltage bulbs come in 4, 7, and 11 watts. The more wattage, the higher the light output. But, you also need a larger transformer to run higher powered lights (more expensive). Spotlights generally use halogen-type bulbs that come in 10, 20, 25, 30, and 50-watt sizes. Again, the higher the wattage, the more light you get, but at increased cost for the transformer.

Personally, I don't care for the solar lights. They usually have one LED in them and they aren't very bright. Sure they save energy. But, they're more expensive and you will need more lights to get a given amount of luminescence. They also put out an artificial looking light, because they come in either bright white or amber (trying to simulate the glow of incandescent bulbs).

Just go to your favorite home inprovement store and look at the lighting packages they have for sale. You should be able to pick up a plastic 10- or 12-light set (several tiered walkway lights, plus a few spotlights, cable, and transformer) for about $120 or so. Although, you may need extra cable and wire nuts for splicing the feeder cable, too.