The Shopify.formatMoney method extracted from option_selection.js for stand-alone purposes.

shopify-money.js

var Shopify = Shopify || {};
// ---------------------------------------------------------------------------
// Money format handler
// ---------------------------------------------------------------------------
Shopify.money_format = "${{amount}}";
Shopify.formatMoney = function(cents, format) {
  if (typeof cents == 'string') { cents = cents.replace('.',''); }
  var value = '';
  var placeholderRegex = /\{\{\s*(\w+)\s*\}\}/;
  var formatString = (format || this.money_format);

  function defaultOption(opt, def) {
     return (typeof opt == 'undefined' ? def : opt);
  }

  function formatWithDelimiters(number, precision, thousands, decimal) {
    precision = defaultOption(precision, 2);
    thousands = defaultOption(thousands, ',');
    decimal   = defaultOption(decimal, '.');

    if (isNaN(number) || number == null) { return 0; }

    number = (number/100.0).toFixed(precision);

    var parts   = number.split('.'),
        dollars = parts[0].replace(/(\d)(?=(\d\d\d)+(?!\d))/g, '$1' + thousands),
        cents   = parts[1] ? (decimal + parts[1]) : '';

    return dollars + cents;
  }

  switch(formatString.match(placeholderRegex)[1]) {
    case 'amount':
      value = formatWithDelimiters(cents, 2);
      break;
    case 'amount_no_decimals':
      value = formatWithDelimiters(cents, 0);
      break;
    case 'amount_with_comma_separator':
      value = formatWithDelimiters(cents, 2, '.', ',');
      break;
    case 'amount_no_decimals_with_comma_separator':
      value = formatWithDelimiters(cents, 0, '.', ',');
      break;
  }

  return formatString.replace(placeholderRegex, value);
};

This was exactly what I was looking for and works like a charm, you sir are an absolute legend.

there was a slight error in the code

function formatMoney(cents, format) {
  if (typeof cents == 'string') { cents = cents.replace('.', ''); }
  var value = '';
  var placeholderRegex = /\{\{\s*(\w+)\s*\}\}/;
  var formatString = (format || this.money_format);

  function defaultOption(opt, def) {
    return (typeof opt == 'undefined' ? def : opt);
  }

  function formatWithDelimiters(number, precision, thousands, decimal) {
    precision = defaultOption(precision, 2);
    thousands = defaultOption(thousands, ',');
    decimal = defaultOption(decimal, '.');

    if (isNaN(number) || number == null) { return 0; }

    number = (number / 100.0).toFixed(precision);

    var parts = number.split('.'),
      dollars = parts[0].replace(/(\d)(?=(\d\d\d)+(?!\d))/g, '$1' + thousands),
      cents = parts[1] ? (decimal + parts[1]) : '';

    return dollars + cents;
  }

  var match = formatString.match(placeholderRegex);

  if (match) {
    switch (match[1]) {
      case 'amount':
        value = formatWithDelimiters(cents, 2);
        break;
      case 'amount_no_decimals':
        value = formatWithDelimiters(cents, 0);
        break;
      case 'amount_with_comma_separator':
        value = formatWithDelimiters(cents, 2, '.', ',');
        break;
      case 'amount_no_decimals_with_comma_separator':
        value = formatWithDelimiters(cents, 0, '.', ',');
        break;
    }
  }

  return formatString.replace(placeholderRegex, value);
};