i will try and answer all the questions. as far as how much i am not sure you can check on their website. i am pretty much family at the hannemann household so my price would not apply to you..haha..
they are three inches wider on each side. it opens the stock wheel well more than the inner fender. the fiberglass fenders are made to get rid of the inner wheel well but i decided to keep them. i just beat the crap out of them with a hammer until they kind of fit and used weather stripping to fill in the gap.
the fenders are strong as hell. they will take way more to break than the stock ones. i hit trees and stuff all the time not even a scratch. they do flex a bit also. these things are bad. they look sweet. i am working with harold hannemann to make some rear panels for the k5 but it looks like i might have to do most the work myself.
if there are any more questions feel free to ask.