Bumpers can be pricey and usually are not below $500 like tjkj said. You have to think of a new bumper as more than just a cosmetic upgrade. Lets take the ARB or Rock Lizards stuff for example, standard bumpers are simply attached in a manner so they will release easily during an impact so the crumple in to help slow the vehicle down, this is why you NEVER try to tow a vehicle by the bumper (
http://www.youtube.com/watch?v=5z9gkE0GFb8 ). The ARB and Rock Lizard are attached directly to the frame so they become a direct "heavy" extension of the vehicle, that means it can be a tow point or a piece of armor for the front of your 4x4 (
http://www.youtube.com/watch?v=4niGrPZ7Omc ). A new bumper will also improve your approach angle And at least with the KJ it will also allow you to have larger wheels without trimming away a ton of plastic on the stock bumper to decrease rubbing. A new off road bumper is nothing like new tires, wheels or a lift kit which are all manufactured by machines in a factory, right now as you read this there is a machine being feed a near endless length of steel rod which it curls into a coil and cuts off so it can make the next one. Even if the pieces are cut by a computerized machine it still requires a human to lay each piece onto a form and go around making sure it all lines up right and weld it by hand, thats where the cost of off road bumpers come from.
In conclusion any good off road bumper is an important piece of equipment, it protects your vehicle, acts as a tow point and also lends itself as a good place to lift the vehicle via a hi-lift.
So when you order your new Rock Lizard KJ bumper just remember that he is sweating away hauling steel plates around and dealing with the heat of a cutting torch and welder.
thats my two cents.