Is it possible to change the PayPal prices to fit a particular email address?

I would like to know if I can set up PayPal to immediately change the prices based on the email provided for our form here. We haven't added the PayPal feature because we offer lower rates to a specific company.

Yes this is possible using conditional rule and pass the calculation to a payment field. 

Follow these steps:

1. Create a conditional rule that will update a form field value when conditions are met. You can set something like "If email field is Equal To @domain.com" field value of your calculation form widget will be updated.

2. Create a calculation field using Form Calculation Widget. It can be found under "Widgets" section.

3. Follow this instruction on how to pass calculation value to a payment field.
4. Please take a look at this sample. So basically you can put different emails with different rates.