Relative to most other modifications that you could do to your car, a cold air intake is comparatively inexpensive. The more entry-level kits could be had for around $150. All the while, higher-spec cold air intakes that are more suited for high-performance cars might run you as high as $500. On average though, most of the good ones are selling with a $300 price tag or thereabouts. When you consider that it's able to add upwards of 20hp and an additional 3-5mpg (not applicable all the time, as it's also dependent on your vehicle), getting one fitted to your car might be worthwhile.