function ff_PayPalSelect_action(element, action)
{
    switch (action) {
        case 'change':
	    if(element.selectedIndex > 0)
	    {
		// price|tax corresponding to the PayPalSelect values
	    	var prices = ['60|3', '100|5'];

		// name of the select or textfield that holds the multipliers
		var howmanyName = 'howmany';

                var howmany  = ff_getElementByName(howmanyName).options[ ff_getElementByName(howmanyName).selectedIndex ].value;
		// or use this if you use a textfield for the multiplier instead of a select, in that case, comment the line above and uncomment below
                // var howmany  = ff_getElementByName(howmanyName).value;

		// calulations and re-assignment of prices and taxes
	    	var val = prices[ element.selectedIndex - 1 ];
		var splitted = val.split('|');
                var result = Number( splitted[0] ) * Number( howmany );
		var taxes  = Number( splitted[1] ) * Number( howmany );
		var selector = element.options[ element.selectedIndex ].value.split('|');
		element.options[ element.selectedIndex ].value = selector[0] + '|' + selector[1] + '|' + result + '|' + taxes;
	    }
            break;
        default:;
    } // switch
} // ff_PayPalSelect_action

function ff_ELEMENTNAME_action(element, action)
{
    switch (action) {
        case 'change':
        // setting back PayPalSelect to initial state
        ff_getElementByName('PayPalSelect').selectedIndex = 0;
        break;
   }
}

<script type="text/javascript">

function paypaySetAmountValue()

var addVenue1 = document.getElementById('addVenue1')
var addVenue2 = document.getElementById('addVenue2')
var addVenue3 = document.getElementById('addVenue3')
var addVenue4 = document.getElementById('addVenue4')

if (addVenue1 == !checked && addVenue2 == !unchecked && addVenue3 == !unchecked && addVenue4 == !unchecked)
  {
  paypal.amount.value == "469.95";
  }
  
else if (addVenue1 == !checked && addVenue2 == !checked && addVenue3 == !unchecked && addVenue4 == !unchecked)
  {
  paypal.amount.value == "694.95";
  }
else if (addVenue1 == !checked && addVenue2 == !checked && addVenue3 == !checked && addVenue4 == !unchecked)
  {
  paypal.amount.value == "919.95";
  }
else if (addVenue1 == !checked && addVenue2 == !checked && addVenue3 == !checked && addVenue4 == !checked)
  {
  paypal.amount.value == "1144.95";
  }
  
else 
  {
  paypal.amount.value == "244.95"  
  
</script>