im trying to get my calculated total to show up when you checkout at google

I added the question marks in the value because thats what i need help with, since the Value changed per customer, i need it to self update itself, i have also included the code for my total box, and the script that totals all my radio and hidden buttons, I did not include my form, because i saw it as irrelevant

Google Checkout button code:

Code:
<input name="item_name_1" type="hidden" value="Custom Desktop"/>
<input name="item_description_1" type="hidden" value="Built by us for you"/>
<input name="item_quantity_1" type="hidden" value="1"/>
<input name="item_price_1" type="hidden" value="????????"/>
<input name="item_currency_1" type="hidden" value="USD"/>
<input name="_charset_" type="hidden" value="utf-8"/>
<input alt="" src="https://checkout.google.com/buttons/buy.gif?merchant_id=**************&amp;w=121&amp;h=44&amp;style=white&amp;variant=text&amp;loc=en_US" type="image"/>
Total Script:

Code:
<script>
  function updateAmount(){
 var inputs = document.getElementsByTagName('input');
 var total = 0;
 for(var i = 0; i < inputs.length; i++){
 if((inputs[i].checked || inputs[i].type === 'hidden') && !isNaN(inputs[i].value))total += parseFloat(inputs[i].value);
 }
 document.getElementById('txtTotal').value = total.toFixed(2);
}
window.onload = function(){
// get input elements
 var inputs = document.getElementsByTagName('input');
// loop inputs
 for(var i = 0; i < inputs.length; i++){
// check type for radio ifso set the updateAmount method to the inputradio onclick event
   if(inputs[i].type == 'radio')inputs[i].onclick = updateAmount;
 }
// start price update function unload
updateAmount();
}
</script>
Total Box Code

Code:
<td width="25%"><input name="Text1" id="txtTotal" type="text" /></td>