PayPal via their buttons tools (through a regular PayPal account back-end) supports a subscription button that allows you to specify an initial charge and then the ongoing subscription charge (so the initial charge is for a "trial period", and then the subsequent ongoing charge which is a different amount). This is discussed here
https://www.paypal-community.com/t5/Merchant-services-Archive/One-ti...

Since this add-on already has pretty much everything else you can do, I'm thinking you could probably implement this as well. Any chance of that happening?

Type:	Discussion
Status:	On Hold