Hey Steve, good question. Yes you can definitely monetize free sites. By your Wordpress account I'm thinking you're meaning Wordpress.com, not Wordpress.org?
My problem with your question is, why do you not want to use affiliate marketing? And I wouldn't put links directly to affiliate products, especially from these sites. What I would do is use these sites to build a following, send people to a "squeeze page" (aka opt-in page), where you offer a free gift, eg ebook, video course, audiobook etc. You ask for their email address to send it to them, and then you capture the email in your list, send your list automatic emails as well as broadcasts, and make more money like this.
The benefits of this compared to what you're describing is that your email list is YOURS. Nobody else's. Nobody can take that away from you. You can save it, and even if the autoresponder company you were using crashed, you could still use those emails. The problem with other websites is that they can ban you at a moment's notice, permanently, without warning. You lose all your followers, and you have to start from square one. Also, people who do visit those sites will possibly never see you again. However you can continually offer affiliate products to people on your email list over and over. And you can sell it, and build a relationship with them, which really helps with conversion rates and CTRs (click through rates).
If you want some more detail on how this email marketing works (affiliate and selling your own products, ie vendor), I can paste a post I've just put elsewhere laying it all out step by step.
If you still want to go ahead with ads on these free sites instead, I can't really help you there unfortunately as I don't have experience with that (only Youtube ads, and the general rule of thumb for that is 1million views = £1000).
All the best!
Cam