Customized Paypal form

We are looking for a customized Paypal form for a client website we are designing. The client is selling personalized trinkets with quotations or sayings on them - the customer can select from a list or provide their own. The trinkets come in several packages with different quantities, and the client needs customers to be able to select multiple sayings (up to 10). AJAX or something similar is preferred to make new form fields appear for multiple sayings (i.e. "Click Here to add another saying" - similar to the adding of multiple attachments in Gmail).