Bring USD, and exchange to Pesos at any currency exchange. Never pay with credit card (unless you have to). In Argentina there is the "blue dollar" which means you will get a better rate exchanging cash. Credit cards use the official exchange rate, which means you will pay ~2x more if you pay with CC.
Within Mar del Plata, the easiest way to travel is by walking or by cab. Taxis are pretty cheap and inner city busses are very complicated.
If you plan to do some travelling in Argentina, the easiest and cheapest way is by bus or plane. There are many overnight bus options available.
-Buenos Aires: Capital City - Very European-esque. Best place to see Tango. -Cerro de los Siete Colores (hill of seven colours): Uniquely coloured hills in the north of Argentina. -Salinas Grandes: Salt flats between Salta and Jujuy. -Carilo and Mar de las Pampas: Upscale, small beach resorts -Mendoza: Wine country and the highest mountains in Argentina - Aconcagua is here. -Iguazu Falls: On the border with Brazil. Massive waterfalls -Ruta de los 7 lagos (seven lakes road): Beautiful drive in the northern tip of Patagonia - Near Villa La Angostura and San Martin de los Andes (beautiful towns) -Bariloche: Cute mountain town in Patagonia - very Banff-esque. Near Frey. Excellent chocolate. -El Chalten: Location of the famous Fitzroy range -Ushuaia: One of the southernmost cities in the world. Lots of glaciers and you may see Penguins.