The real issue is simply that the cost for Truvada oral tablet (100 mg-150 mg) is around $1,564 for a supply of 30 tablets. In the US, the patents expire in 2021.
No, $1,564 is the price when bought through US pharma. They're available via the site recommended by https://www.iwantprepnow.co.uk/buy-prep-now for $80. So, presumably the cost is more like $20 or so.
What makes you think this spammy affiliate marketing site is sending you to online pharmacies that will actually send you the drug, rather than take your money and send you nothing?
This "spammy affiliate marketing site" is neither spammy, nor does affiliate marketing. It saves hundreds, if not thousands of lives. Read the linked article.