This will do the trick. I have only supplied the all important convert function. I leave to you to wrap what ever code you require around it.

use LWP::Simple;

...
sub convert {
    $_=get("http://www.oanda.com/converter/
          classic?value=$amount&exch=$fc&expr=$tc");
   s/^.*<!-- conversion result starts//s;
   s/<!-- conversion result ends.*$//s;
   s/<[^>]+>//g; s/[ \n]+/ /gs;
   print $_, "\n";
}
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mitd - Made in the dark.