Anyone know where....

Does anyone know where I could get a cheap or free (doubt it) billing product.

What I mean is, I run all my payments for hosting through paypal, but I need a cheap or free product that will allow people to signup for the packages, which will then enter there details into a database, so myself and my staff can see exactly what they want, and set it up for them straight away, whilst the customer pays using paypal.

A nice example of such thing is PHPCoin. But if I keep PHPCoin, I would like to embedd just the order page into the website. I don't want invoices, and client login to a system that isn't needed.

Any help?