DaveW and the other boardgamegeek poster are both correct. You are unfortunately not. The Supplement is quite clear that a player doesn't have to make a mandatory action possible. Thus, you do not have to pay the uproot cost to make a mandatory move action possible. The section about paying the costs attributed to the action is not relevant to the discussion, as uproot is not a cost to move. It is a cost to get rid of the rooted trait, paid for at the beginning of the creature's activation. This may seem like semantics, but it is an important distinction.
Now, if this was a question regarding Suppression Orb, which DOES add a cost to move actions, then you WOULD be required to still move if you could pay for it.