Well, I've always been charged less, but my last farrier refitted once (when I'd booked him in for new - I wasn't there) and I didn't get charged any less
Think its about a tenner less for us if its all round and a fiver if its just fronts or hinds. Although hardly ever apllies to my nag just the poncey dressage horse we have on yard!
My lad always has new shoes as he has normally got considerable wear on the old ones. Shoes are quite cheap to actually purchase so you will never get a tremendous reduction in price, but it takes the same amount of work to square up, reshape, trim feet & fit as is does with a new pair. IMO it's hardly worth bothering with a refit