Suspension Lift Options

I am looking into buying a 2003-2006 Chevy Silverado 1500 4X4 Extended Cab. I am planning to lift it, but have heard some mixed opinions on my options. I have been told to avoid torsion key/block set ups, as the torsion keys tend to lose tension and cause sag. I want between 2 and 4 inches of lift, but want to keep it relatively cheap. I am planning on keeping the stock rims, and just adding larger tires. I know there are some people on here who could help me out, and prbly know more about certain things than I do. So..in a nut shell, I want a way to get 2-4 inches of lift out of a 03-06 Extended Cab Chevy Silverado 1500, but I also want to keep it on a budget.

Thanks for all the help guys,
Tyler