[Plugin: Simple Cart & Buy Now] Processing Fee

I would probably just use the ‘shipping’ field, depending on the structure of your fees. If you look at customize.php under templates/YOURTEMPLATE it is structure to allow for you to run your own code for pricing (if total<$100, shipping=$5, if total>100, shipping=$10, etc) and then that fee will be added when they make the purchase with google or paypal. Or you could use the shipping as a template and extend the plugin to have a second ‘shipping’-like field called ‘fee’ or the like.