I read the Skins have 28 mil in cap space once they cut RG3. So tagging him eats up 20 of that 28 million. That's a large cap hit for someone you're trying to make "prove himself".
You'd be better off working a long term deal with a lower initial cap hit with certainty of your QB.
Well, if this were a one way street, sure. But Kirk and his people may not want that. Which is why they have this impasse.
Also, the Skins have a couple guys like Andre Roberts, Culliver and Goldson who were really just not that good this past year that they can cut and save an extra 10 mil or so from the cap.