No, you don't have to pay anything! They're both free. Maybe you clicked to download 'Ad-Aware SE Plus'...that one costs $.

Ad-Aware:
Click on that link in my last post, then click the 'home' tab on the Lavasoft page. In the top right corner you'll see an option to download Ad-Aware SE Personal...download that. I've been using it for ages. To update, click on the blue world icon.

Spybot S&D:
Click on the link in my last post & choose a mirror to download (try any one).
To update, click on the blue world icon.

I use them both. Just remember to update before doing a scan. The help options (you'll see it on both) have lots of info about how to use the programs.