how to add custom field with price to checkout process

[jdsilva]

I don't know if it is possible with shopper fields etc..

what we do is add some custom code to the checkout template to provide a add to cart button for a specific product (Giftwrap - whatever)

I guess this idea perhaps could be extended to provide a text field for a message

see ->  http://test2.gjcwebdesign.com/fish/index.php?option=com_virtuemart&view=cart

At GJC Web Design, how did you accomplish this feature?

[Studio 42]

YOu can accomplish this using a module displaying a product and call this directly and check if the product is already in the cart or not.
Of course this need some coding. But perhaps a module exist for this ?