Create on html page a 'add to cart' function-call link.
This will activate a php and add product from call function to a shoppinglist (visible on page)
This shoppinglist will show products ordered and total to pay excluding shippingcosts. (dynamic)
When customer decides to proceed with checkout he fills his shippinginfo and costs for shipping are calculated.
After this he can decide how to pay, either by bank or by paypal etc.