It is ridiculous that corporations with profit margins high enough to bring the likes of Pablo Escobar out of the shadows perpetuate their journal title monopoly off of the university-funded labor of academics, and yours is a useful way to push back. One comparison for academic journals is with academic books, where often the publisher does pay a few hundred dollars to a reviewer, and that has continued even though profit margins are getting much thinner for academic books (I think). So if you can't devote your free labor to low-cost journals that provide their articles freely, yes send them a bill or just refuse to review for them (as I often have for going on nine years http://www.openaccesspledge.com/)