OK another way perhaps, where customers can pay you a 'random' amount, let say a bunch of monthly invoices by credit card.
Still use Paypal as your payment gateway but make sure Paypal has been upgraded to accept credit cards for the 'non paypal' customers.
Here is an example
http://www.harrisand.co.uk/payment_page.php
If you look on the right hand side you'll see payment instructions, fill in the form, generate paypal button, a paypal button appears, click it. You are taken to Paypal where you can sign into paypal or if you don't have a paypal account make a payment by credit card. Feel free to test it but stop at the credit card info page..lol
Paypal is secure as you know
I got the code from Naval Design
http://www.dbtechnosystems.com/ cost just a few $$$'s but well worth it.