I assume you are using a Cell with a Foreign Contact as an SMS messages wont cost more than about
$ 0,20with a local SIM
... If you consider this expensive then start hording some 'monedas' and sell them on the Black Market for 3 - 8 % more that their face value to subsidise your texting !
Found the following here:
http://foros.3dgames.com.ar/dispositivos-moviles-y-telefonia-celular.123/219591.cual-es-direccion-e-mail-sms-movistar.html
They suggest that Movistar charges the person that receives the message !!!
* La de CTI es @sms.ctimovil.com.ar
* La de Personal es @personal-net.com.ar
* La de Nextel es @nextel.net.ar
Si es @sms.movistar.net.ar el problema es que te cobran $0,12 por cada mensaje que recibis