Check out the Hydro Steering Bible on Pirate... it's good stuff:
http://www.pirate4x4.com/tech/billav...ing/index.html
If you can figure out your needs and how you want it to handle(turns lock to lock, etc), you can choose parts that fit your needs and save big money over any kinds of kits.
www.surpluscenter.com has cheap hydraulic rams that lots of trail-only guys commonly run without issue.
If it is NEVER driven on the street, then I would modify your stock pump, buy an orbital from PSC or somebody(quality orbitals are not that expensive compared to cheaper ones), and a Surplus Center ram. If you drive it on the street more than 25mph, then I'd spring for a good double ended ram from PSC with heims so there isn't as much/any slop in the steering.