There isn't a fixed value for XRP because it will price itself at a rate high enough to support it's ability to handle ripples transaction capacity.  Its value is derived from the value of the other IOU's stored and traded within the ripple platform.  Outside of ripple it has much less value since it requires trust in the ripple system, which one would not likely be extending if they were not actively using ripple for its intended purpose.  Within the ripple system it's extremely versatile though.