Some common internet samples...

Missulu forms are billed as follows:
Downloading of forms is completely free of charge.
To use the forms without processing, simply remove the fields on your form that are of the type 'hidden'.
However, if we process the forms, sending user results and logging them in the 'myaccount' page, we have a two tiered program. The price is either $9.95 per month, or $0.01 per response, depending on which is greater based on a one month period.
The amount due will be displayed in the 'my form results' page accessed from 'myaccount'.
The balance is due the first day of the new month.