The premiss is simple:
Paypal subscription managed users, when subscription is not paid for, PayPal IPN automatically closes account. If possible, payment is to be split to 2 PayPal accounts.
User selects a variable from a remote database (drop down list?) and enters a value they wish to be notified of. User can create as many notification requests as they want.
Queries are run against remote database every 60 seconds.
When variable value is matched or passed on remote database the user is emailed.