PHP add to cart shortcode for Dynamic Price

I run a growing printing company.
I have a website on WP where customers upload a file and a script calculates the price and gives it a unique time stamp ($myFileName, $myPrice)

They then have the option to add to cart and purchase.
I have got this too work using the WP Ultra Simple Paypal Cart plugin.

unfortunately I don’t have any control or visibility of transactions or can send an automated email to confirm order.
All this is taken care for with Paypal.
So I’m looking to upgrade and want a Cart where I can track orders, and send automated emails .
I wish to use WP Ecommerce. and want to know how I can add a shortcode in my PHP to have add to cart when the item generates a price.

Here is my PHP for add to cart`[insert_php]

global $myResponse;
global $myPrice;
global $myFileName;
echo $myResponse;
if ($myPrice > 0) {

<strong>echo print_wp_cart_button_for_product($myFileName, $myPrice);</strong>

}

[/insert_php]

If I install WP eCommerce how can i swap out
`
echo print_wp_cart_button_for_product($myFileName, $myPrice); for it to work, I can’t find a way to do this.
I welcome any help

Kind regards

David

https://www.ads-software.com/plugins/wp-e-commerce/