You'll certainly be understood speaking 'Spanish' Spanish but expect some wry smiles from people who believe that that 'old-fashioned' accent is really funny to listen to.
Also - it depends very much on where you're going. South America is huge, and the accents vary from region to region as well as country to country. Having travelled in Peru years ago, and picking up the language bit by bit as I went along, I was told subsequently that I had a Peruvian accent when I went to Spain. (Very flattering!)
But the strongest differences are in Argentina, Paraguay and Uruguay, where they speak 'rioplatenense'... words, pronunciation and meanings change. i.e. 'Villa' is pronounced "Beezha"; 'usted' becomes "voze"etc etc... Don't worry, you'll be understood, and quickly work out what peple are saying to you.
Don't expect to speak or understand aword of Portuguese - but that mustn't stop you seeing Brazil.
If you're as broke as you say, this is probably a good time to be in S. America. Sadly, their economies are in real trouble.