I have a bastard leaf pack in the back of mine, basically a stock pack with a leaf or two taken out and others added, one from a Toyota!!! in there somewhere I think.
Cost was pretty minimal, I also have extended shackles but that was more for additional lift. Anyway, you can see even with a cheapass leaf pack it flexes well and is pretty balanced with the front. Also carries a load well. I'd say if you're tight on cash try picking up a second leaf pack and putting something together, also google bastard leaf pack.
Cheers
Steve