I have been waiting for someone to develop a paypal subscriptions mod. But there has been no development that I know of, so I modified the existing Paypal subscription module.
Basically, I only changed the way in which the payment page is called. I will have a relatively small number of students (<80) on my site. So I didn't make use of the IPN (PayPal username) function.
This module will work exactly like the old one... but instead of having to make a single payment, the user has to make a subscription, if this is created successfully, he is sent back and enrolled... When a user cancels a subscription, PayPal will send an email, alerting you of the subscription. It is then up to you to manually unenrol that user.
I know this is not the most graceful way of doing this, but it's the only way I can manage...
This has not yet been tested, as I cannot send payments to myself. But it will be tested shortly...
If anyone is interested in getting this mod form me, please reply here.
Hope this can al least be the start of a brand new paypal module.
PS: It has only been tested on Moodle 1.5.4