Well, the "short cuts" can be stitched up with picture hanging wire. As for the lnb, it might still be good. However, you might be better off replacing the whole thing with an LNBF.
As for the $100, that's not out of line if the dish is at least a 10 footer, and otherwise seems in fairly good shape. Take cash, and try to offer him a bit less. Maybe $20 dollar bills, and give it the "used car" overlook, then the, "Well, it has a few issues (tears, maybe bad lnb, etc) would you take..." and go from there.
Of course, don't let him see the entire $100, keep some of it in another pocket when you pull out what you'd really like to get it for.