Paypal addon without a dev licence ?

No. Add-Ons are not available individually. The more complex Add-Ons such as the PayPal and User Registration Add-Ons are only available to Developer License holders. This is because they are more complex and typically require more support along with more knowledge on the part of the enduser to properly implement.

We opted not to sell them individually because we would have had to price them in such a way that the PayPal Add-On itself may have actually been more expensive than a Personal License of Gravity Forms itself, which just doesn't make sense from an end user standpoint. But from a support management standpoint it would have been necessary.