So simply...
1) params the paypal plugin to your paypal account
2) create the diffrent packages
3) customer select a package, click on pay now, he is redirected to the paypal payment page, payment done, he is redirected to the site and then the package is added to his account. If not done, package no added...
for have a more complete idea, go on the demo site
joomloc.fr.nf/lbvehicles/ login with : demo/test here
joomloc.fr.nf/lbvehicles/fr/component/users/
when connected, on the left user menu, click on "my ads account", then click on the "subscibe to package" tab, click on subscribe to a "not free" package, when select click on "pay now with paypal" BUT DO NOT PAY IT I IN REAL SITUATION, but that give you an idea, on the paypal ayment page click on "cancel and back to..." it is the same when payed but action is to valide package...