Sheila has those big radiant gas overhead heaters in her studio in the US, and they work great, but I have been on Tom's balcony, and that heater is a bit of overkill.
Plus, 18,000 pesos plus installation?
this style, of electric radiant heater, is cheaper and easier to install- but still pricy.
http://articulo.mercadolibre.com.ar/MLA-606728630-calefactor-electrico-para-exteriores-termoray-cosi-xl-2000w-_JM
i think you need to consider one of those lampost style ones they have in restaurants- those are about 5000 pesos, and totally portable, and you can change the tanks yourself.
what you want is called a calefactor (heater) exteriores