I have a JD950 that I've been wondering the same thing. The manual at least implies that there's a field upgrade to add power steering but I've never got around to asking the dealer. No budget for it anyway. When I got my first Surplus Center catalog a few weeks ago I got to thinking that with some study it'd probably be possible to plumb something up even if the dealer didn't have anything.
I'm thinking about the same thing for my7100. Someday when time allows I'll go to an auto wrecker and see if any of the units would be adaptable to the tractor. I'd plan on using the tractor hydraulics rather than installing a power steering pump. There's gota be a way or so my elbows tell me.
Egon
I Have a John Deere 850 and was quoted a price of approx. $850.00 for a power steering kit. I was told that power steering was a dealer add-on for my model.