Jonathan,
You CAN do this yourself. I did mine, by myself, in the driveway. And I don't consider myself an accomplished mechanic, although I've done a few 'medium-large' jobs on vehicles in my lifetime. (Everyone will have a different connotation about what size work that means... )
If you have typical tools, jackstands, and a floorjack that you're comfortable with (and that will handle the weight of the Cummins), this job isn't hard. The most difficult part for me was getting the lower control arms bolted back up. That's because I unbolted them at KORE's suggestion when the new springs wouldn't slip in *easily*. I think they might have gone in without loosening the control arms if I'd been a bit more ingenious. As it were, re-attachment of the anti-sway bar pulled the control arms right back into alignment by lowering the axle slightly.
If you do have a shop install, they will probably quote you numbers based on hourly rates - if they will quote a fixed-price at all. I couldn't pin down any of my local people, mostly because this type of suspension was "new" to typical 4WD shops at the time I purchased. The first question out of the telephone when I asked was "What kind of lift is it?" I had printed the installation instructions, and all the nice pictures from the KORE website (then T-Rex), but they still wouldn't give me a hard-dollar quote. This type of aftermarket componentry still isn't in the mainstream of 4WD custom work.
I'd say you'll have to take the estimates here on TDR as best-guess. Average them, and use that as your budget.
But, if you're like me - after getting the kit, you won't trust the install to a 4WD shop anyway. These parts are too nice to let some grease monkey bugger them up!!
Good luck with it,
John