Here's a lil' video on how screen tones in manga are done. It's pretty acccurate and it's the true. By the way, manga materials are like, not really cheap if you wanna make a 40-45 pages long manga chapter. And that's just it being a oneshot. Imagine making a whole long-running manga series. It's gonna cost quite a lot. And if you don't get picked up by a manga agency right away, and keep trying, and trying, it's gonna like, be soo expensive. But then if you get picked up one day and you're like the happiest person in the universe cuz you're gonna get serialized for real, and your manga is gonna be published like you've dreamed, and then it's just not popular enough and you get taken down. That's pretty fucked up. Yikes! Ahem! So as Joey (video boy) said - have making manga as a side job or at least have a part-time job so that you can get by somehow. After all, making manga is not the most profitable job in the world unless you're like giga mega pro in the manga world.
***skip to 3:43 to see the actual screen toning.***
***skip to 3:43 to see the actual screen toning.***