jeff's math is almost right. You've excluded the fee for Xooming to Uruguay - $17, and the Colonia fare at the Messi dollar is $50 USD.
So $1,067 for the trip to Colonia (and you lose half a day - take the 0900 there and the 1600 back on Colonia Express), vs. $1,280 for local.
That's $213 USD...