Oops! That would be from the U.K.,please.

You should just check with your post office in the UK...they set the prices, not the Argentine post office. There are also companies like DHL or FedEx that operate in both places.
One problem you may have with packages you send is taxes. In my limited experience receiving packages from the US in Argentina is that you have to go to customs, show them all the contents of your box, then pay taxes on the value of whatever you have inside. Luckily, there was no value written on the US post office form attached to my box and there were only clothes and food inside so I didn't pay anything. But, one of the other people there received a fax machine from Spain without a value listed on the form attached...he had a lot of problems!