Love love love the K&N lifetime air filters. They may cost more up front, but you only have to buy it once and you can go longer between cleanings. I won't claim that it increases gas mileage because with my driving habits I wouldn't be able to tell anyway, but I can say that the engine runs smoother and feels more powerful. That's why every time I get a new car, my first upgrade is to swap out the stock air filter for a K&N.