Depends. There are two types of lifts you can do:
The first is IMO crappy and mainly cosmetic where you lift the body but leave the suspension alone. This will give you more clearence in your wheel wells but not help you much offroad. I think the max you can do with this is 4 inches.
The second which is far more expensive but way better is a lift done via replacing parts in the suspension. This lift gives you more flex when you are offroading or doing whatever. The price on this one can vary greatly depending on the company whos lift kit you go with and exactly what you are looking for. I would suggest shoping around at local shops becasue without the right equipment lifting a truck is a huge pain in. These can cost from 500-however much you want to spend. I would probably guess between 1000-2000 for good prices stuff and labor, if you shop around.
Lastly, don't forget to get an alignment done after you get a lift because you are probably getting new tires with it and they will get eatten up fast. You might also want to get your speedometer adjusted after the new tires too, cops don't like the "but I made my car big and abonoxious, so I had no idea how fast I was going, sir"
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