I have been making money online for over a year now. Not in the big time yet, still consider myself to be learning my craft. I was doing it really ineffectively (using adsense and amazon along with a t shirt affiliate deal) and driving traffic almost exclusively though facebook. Probably averaged about $800 a month over the last year, mostly because Christmas brought an absolute ton of t shirt sales)
You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.
If you live in an area where Uber or Lyft operate, why not become a driver? If you're looking to make some short-term cash, you can definitely rake it in by working for one of these popular car-hire apps. As long as your vehicle fits within the specifications of their program, and you have a clean license, you could do this on the side, especially if you're in a crunch for cash.
Build up a following on your Instagram account and you could quickly be making extra money online. Major brands, gear companies, and even startups are willing to shell out $500-$5,000+ per post to get in front of your audience. While it’s getting harder and harder to build a massive Instagram audience, if you already have a solid niche and are posting quality content regularly, with a few small tweaks you can make yourself an influencer. Check out this awesome article from Shopify on how to build and grow your Instagram following to get started.
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.