It's one of those things that the higher dollar cards are obviously at a premium, and unless the person offering it is dying to unload it, you likely would have to give up some value (within reason). Unless it's a roughly even swap (i.e. Thundermaw for Sublime Archangel or Cavern of Souls, etc) i don't think it's unreasonable to expect.
I know that I've received countless offers for 2-3 five or six dollar cards that are comprised of like 1-2 one dollar cards and a bunch of junk rares/uncommons. In those instances, I'm VERY unlikely to do the trade unless I'm picking up a LOT of value. I've instituted a rule that I go by low values (because 1. you could just go buy them at that price, and 2. it doesn't inflate the values of penny cards) and that the person trading up will have to give up value. I get that you have to start somewhere, but man...