Lots of info using the SEARCH function. This has been discussed many times before.

The cheapest lift is using OME912 springs in the rear from either of these guys.
http://www.darlington-offroad.com/
http://www.independent4x.com/
Both are great to work with and very much into supporting the Isuzu community.

The springs will give you 2" - 2 1/2" of lift (more with a spacer.) Then you need to crank the front torision bars up to match. Re-align the front end and you are good to go.

There are many other options such as ball-joint flips to help with alignment if needed, front axle drop brackets to help with CV angles, etc.

For a mild lift (2-3") you DON't need to change the shocks unless you want more droop when flexing.