01 Tahoe leveling kit

[Fairlyoddchild]

So my friend has an 01 tahoe that he wants to put a leveling kit on. By no means is he a mechanic, that's where I come in. I told him I'll do the research and installation if he buys it and he agreed. I've never done a leveling kit before and I was wondering what you guys would recommend. I've seen ads for torsion bar keys, spring spacers, taller springs, whatever. I'm just looking to see what I need to get for him and an approximate price.

Thanks