Mystery solved. No difference whatsoever.
If I get a Dollar from Uruguay and convert it to pesos ,,,,, current arbolito rate is 1285.
If I stay home in BsAs and WesternUnion myself a Dollar ,,, current WU rate is 1288.
Doesn't make any sense going Uruguay. Strictly from the economic sense. (Not to mention the huge risk carrying large sums of cash across borders and wasting a whole day)
Bottom line ,,,,,, WU rate = arbolito rate.
For a big item purchase Uruguay is not better than WU.
Is there a better way for $10000 US?