1978 was a big year in Argentina. They hosted the World Cup, and many different commemorative coins and medals were issued. The Argentinian Mint issued several denominations with the 'uplifted hands and soccer ball' symbol on one side and various patterns on the opposite side. The large denominations were issued in silver, and that makes them more valuable than 'normal' face value:
20 PESOS: aluminum-bronze, worth face value
50 PESOS: aluminum-bronze, worth face value
100 PESOS: aluminum-bronze, worth face value
1000 PESOS: 0.289 troy ounces silver, worth more than face value
2000 PESOS: 0.434 ounces silver, worth more than face value
3000 PESOS: 0.723 ounces silver, worth more than face value
To find the value of your 1977 or 1978 1000, 2000, or 3000 pesos coin, multiply its silver content by the current price of silver. At this writing, silver is trading at $17.30 US dollars per troy ounce. But the price of silver changes continuously, so you must look it up (click to kitco.com). Today, then, a 3000 pesos coin is worth 0.723 x 17.30 = $12.50 and a 1000 pesos coin is worth 0.289 x 17.30 = $5.
If your coin is in excellent, fully uncirculated condition, you can add a dollar or two to the basic value because collectors are willing to pay a premium for uncirculated coins.