2
The closest there is is a subscriptions module and the xAsset module, both of which support payments by PayPal at the very least. Search this site for the mods. You may be able to extract the payments processing from them.
One or other of these mods requires you to pay a license fee to use the payments processing. As an alternative you may wish to explore integrating commercially available payment processing software into your XOOPS site. The bottom line is that you are probably going to have to pay to get payment processing, which is not unreasonable given that you expect payment for your goods
edit -- PS, you may also want to look at the kshop module. Not sure where payments is with that at the moment.