Creating space for banner ads on your website is another way to generate a revenue from adverts. However for this type of advertising you will need to contact businesses directly and ask them if they would like to advertise on your website. The upside is that you can charge a set amount, or even a recurring monthly fee, to business to promote their services on your site. Using a WordPress plugin like AdSanity is an effective way to manage this type of advertising.
If you have pop-ups and optins on every page, I would have to think that it would be a lot harder to convince someone to link to it. Especially since the pages where you have your optins (and probably receive the most traffic) are probably the same pages that you have your best content on as well that you'd be hoping to pitch in your outreach campaign.