If you're into coding you can find examples on the internet else, you would need to work with a developer. There's no one size fits all script solution, you have define your requirements to get what you need. For instance, check out the Buy Now example below, it has a simple script for shipping choices. It should provide you with some insight as what can be done.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Button Example Code</title>
<!-- START META TAG SECTION -->
<meta charset="utf-8">
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<meta http-equiv="Content-Language" content="en">
<!-- END META TAG SECTION -->
<!-- Start of Script -->
<script language="javascript">
function CalculateOrder(form)
{
if (form.os1.value == "USA" )
{
form.shipping.value = "10.00";
form.shipping2.value = "2.00";
}
if (form.os1.value == "Canada" )
{
form.shipping.value = "12.00";
form.shipping2.value = "3.00";
}
if (form.os1.value == "International" )
{
form.shipping.value = "17.00";
form.shipping2.value = "3.00";
}
}
</script>
<!-- End of Script -->
</head>
<body>
<!-- START SAMPLE CODE SECTION -->
<!-- PARAGRAPH 1 -->
Shipping & Delivery Examples
<br><br>
Buy Now - Script & Combination Dropdown Price & International Shipping Selections.
<br><br>
Widget Book Publishing
<br><br>
<!-- Start of Buy Now Form -->
<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<!-- If using a Business or Company Logo Graphic, include the "cpp_header_image" variable in your View Cart code. -->
<input type="hidden" name="cpp_header_image" value="https://www.yourwebsite.com/logo.jpg">
<input type="hidden" name="cmd" value="_xclick">
<!-- Replace "business" value with your PayPal Email Address or Account ID -->
<input type="hidden" name="business" value="your email address">
<input type="hidden" name="item_name" value="Widget Book Publishing">
<input type="hidden" name="no_shipping" value="2">
<input type="hidden" name="shipping">
<input type="hidden" name="shipping2">
<!-- Replace value with the web page you want the customer to return to after a successful transaction -->
<input type="hidden" name="return" value="http://www.yourwebsite.com/ThankYou.html">
<!-- Replace value with the web page you want the customer to return to after item cancellation -->
<input type="hidden" name="cancel_return" value="http://www.yourwebsite.com/Cancel.html">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="lc" value="US">
<input type="hidden" name="button_subtype" value="products">
<input type="hidden" name="no_note" value="0">
<input type="hidden" name="cn" value="Add special instructions to the seller:">
<input type="hidden" name="bn" value="PP-BuyNowBF:btn_buynow_LG.gif:NonHosted">
<!-- -->
Please Choose:  
<input type="hidden" name="on0" value="Title">
<select name="os0">
<option value="The Big Picture - Hardback" selected>The Big Picture - Hardback - $40.00</option>
<option value="The Big Picture - Cassette Tape">The Big Picture - Cassette Tape - $15.00</option>
<option value="The Big Picture - Hardback and Tape">The Big Picture - Hardback and Tape - $50.00</option>
</select>
<!-- option_index value=0 is associated with variable on0 -->
<!-- option_index value=1 is associated with variable on1 -->
<input type="hidden" name="option_index" value="0">
<!-- -->
<input type="hidden" name="option_select0" value="The Big Picture - Hardback">
<input type="hidden" name="option_amount0" value="40.00">
<input type="hidden" name="option_item_number0" value="WBP-TBPH-1001">
<!-- -->
<input type="hidden" name="option_select1" value="The Big Picture - Cassette Tape">
<input type="hidden" name="option_amount1" value="15.00">
<input type="hidden" name="option_item_number1" value="WBP-TBPC-2001">
<!-- -->
<input type="hidden" name="option_select2" value="The Big Picture - Hardback and Tape">
<input type="hidden" name="option_amount2" value="50.00">
<input type="hidden" name="option_item_number2" value="WBP-TBPB-3001">
<!-- -->
<br><br>
Quantity:  
<input type="text" name="quantity" size="4">
<!-- -->
<br><br>
<input type="hidden" name="on1" value="Shipping Option">Shipping Options:
<select name="os1">
<option value="USA" selected>USA - $10.00 first item / $2.00 each additional item</option>
<option value="Canada">Canada - $12.00 first item / $3.00 each additional item</option>
<option value="International">International - $17.00 first item / $3.00 each additional item</option>
</select>
<br><br>
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_buynow_LG.gif" border="0" name="submit" onClick="CalculateOrder(this.form)" alt="Make payments with PayPal - it's fast, free and secure!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
<!-- End of Buy Now Form -->
<!-- END BUTTON EXAMPLES -->
<!-- END SAMPLE CODE SECTION -->
<br><br><br><br>
<hr align="left" width="50%" noshade>
<br><br>
NOTES:
<br>
In order to test the code, you must replace the "business" value variable with your PayPal Email Address or Account ID.
</body>
</html>
