#2
I've replaced the locking nut on my Ibanez before. Cost like 30 bucks for a new one.

I didn't have that much trouble getting the old one off. I've heard that sometimes the clear coat on the headstock coats over the edge of the nut, and you have to score it with a razor blade or something or the nut will be kinda stuck, though I didn't encounter that problem.

Other than that, seemed like an easy fix to me.
#3
10 bucks to buy a replacement part. I wouldn't imagine that it would be too hard to do.
#5
Well, I adjusted it to be lower. I switched to Ernie Ball 9's and my E is dead at the 5th fret and onward.
#6
30 bucks for a graphite nut, 40 for a bone, 60 for a roller nut.
Fender Highway 1 Fat Strat
Fender MIM Standard Strat(EMG SL-20 loaded pickguard)
Gibson Les Paul Special
PRS SE singlecut
Schecter C-1 Classic
Schecter C-1 Hellraiser
Vox Valvetronix AD50-VT
Fender Blues Jr
Roland Cube 30X
#7
Cost me 35 bucks to get a plastic (i think it was acrylic) nut put on my Ibanez.