Depending on what you're doing, the easiest way to get the currency
symbol is probably Currency:getSymbol().  Printing only two decimals can
be done with the String.format(String) method.  An example:

private static String currencySymbol = getCurrency();

private static String getCurrency()
{
  Currency curr = Currency.getInstance(Locale.getDefault());
  return curr.getSymbol();
}

void doCalculation()
{
  double amount = 3.98 / 1.8;

  outputTextArea.append("%.2f" + currencySymbol, amount);
}

One big caveat: floating point calculations are notoriously inaccurate.  
Instead of using double or float, you should consider using int or long
(and just remember that your values are off by a factor of 100), or use
BigDecimal.  When using BigDecimal, you need to use a MathContext to
specify the precision.  Again, an example:

private static String currencSymbol = getCurrency();

private static String getCurrency()
{
  Currency curr = Currency.getInstance(Locale.getDefault());
  return curr.getSymbol();
}

void doCalculation()
{
  BigDecimal amount =
     new BigDecimal("3.98").divide(new BigDecimal("1.8"));

  BigDecimal roundedAmount = amount.round(new MathContext(2));
  // implicit call to roundedAmount.toString()
  outputTextArea.append(roundedAmount + currencySymbol);
}

This may seem like a lot more work, and in fact it is.  However, if you
use doubles, you're likely to get inaccurate results.  For an example of
what may happen, look for a discussion entitled ".09 instead of .08" in
the group comp.lang.java.help