If you don't have Fantastico here are some other solutions:
phpinvoice
A web-based invoicing and billing solution that is open source and fully customizable.
URL:
http://www.eightballsoftware.com/
PHP Invoice
An account and invoice management program. It supports automated billing through Paysystems, 2Checkout, Worldpay, Paypal, and a custom payment gateway. Customers can login and update their billing info and password, and the admin can send payment due notices to overdue accounts and add accounts manually.
URL:
http://www.phpinvoice.com/
LogicBill ($99 - $400)
A web-based billing application that offers full integration with several payment processors, an integrated help desk, automated invoice generation plus a clean and fully featured interface for your staff and clients.
URL:
http://www.logicbill.com/
hth,
.