Currently there isn't a way to redirect from a store purchase page to a contact form, however, you CAN redirect from a contact form to a product page.
Click the contact form, then click the blue Form Options button. Then click Confirmation, then Link, then select the Product page you want to redirect to.
This will force the visitor to fill out the form before purchasing. You will need to have the product page hidden though, otherwise visitors could find the product and purchase without filling out the form.
