Gonna have to say, not really worth the RP cost, RIOT. Many, many players already have the Santa Baron (myself included) so to spend RP on something that we basically already have (if not a little bit sillier) is just a plain bad idea. It makes no sense from a business standpoint. While the Baron Nashor may be one of the most iconic beasts of the game, unless you make this icon do more than look cool--which, in your defense, it does--you probably won't see too much of your user-base spending RP to get it.
tl;dr: I love you guys, RIOT. But making it cost RP is a bad idea.