The Weebly website building software we use provides a great facility to design and build registration and payment forms. You can inspect a recent sample HERE.
However, if your project requires a few bells and whistles Formstack online software will provide them. We use Formstack online form creation software to build, edit and manage more complex forms.
Formstack forms will integrate with PayPal and various other online payment processors.
Embed your form into your website or use on its own secure (SSL) site. You can also use the 'mobile device' option to display forms in a narrow format.
...Your users will be happy. And so will you.
Depending on the number of forms you create and use, we may recommend that you have your own Formstack account. You can manage it, or we can on your behalf. Alternatively, if you only need occasional online forms, we can build and manage yours on our account.
Terry Alve - Value Websites Limited