Using .htaccess to restrict access to a particular page

I would like to Use .htaccess file settings in order to restrict access to a particular page on my website.
Scenario: I have a page with a form to collect my visitors e-mails in exchage for free event access, on the follow-up confirmation page that follows I will thank my subscriber and also put an attractive offer to buy a paid product at discounted price.
:yum: I need to restrict this follow-up confirmation page acces to only visitors that came from subscription page. in other words: only subscribers can purchase the product on my "thank you" page.
If Thank you page is accessed directly - visitor is re-directed to the subscribtion page.
I believe it's done in a similar way hotlinking for immages is stopped, re-directing visitor to a paticular image.