Can I limit the number of times a product/option can be purchased?

I have PayPal integrated on a form being used for event registration with paid sponsorship opportunities available. On the form, the registrant can select a sponsorship ($800 for example). Is there a way for a paid option to only be available for one selection/registratant? Once that sponsorship level has been paid, I no only want it to be available for selection/or payment (maybe blocked or grayed out signaling not available).

If you're using the payment integration with the "sell products" option then it will not be possible to limit the number of times an option can be selected. 

You may use the "Inventory" widget in order limit the number  of times an option can be selected, but you will need to change your payment integration in order to capture a custom amount, you will then need to perform calculations on your form and pass the amount to the payment field. 

Here's the link to the widget: https://widgets.jotform.com/widget/inventory 

And this guide will help you adding the widget to your form: https://www.jotform.com/help/252-How-to-Add-a-Widget-to-Your-Form 

These guides will help you performing the calculations and passing the amount to the payment field: 

https://www.jotform.com/help/259-How-to-Perform-Form-Calculation-Using-a-Widget

https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field 

I hope this helps.