$150 won't get you quality work, unless you find an artist who is passionate about your project.
Through my own research, quality work generally costs around $20-30 a panel, which amounts to $300-450 for what you are looking for. This isn't even including the price of creating characters which generally go for $50.
So for your panels, you are really looking at $400-550 with only 2 characters showing up (Cider and Darrell).
Of course, you can do this cheaply by using websites like Fiverr, and outsourcing your characters to one person while having another draw the panels.
I don't want to be seen as promoting people whose services I never used, but there is someone who can draw the characters for $15 a person and another who will draw 20 panels for $200. Using them you could have a 2 character 20-panel webtoon for $230.
Of course, this probably won't look nearly as good as the more expensive option, you really do pay for what you get.
I'd also be really wary when searching for artists and find someone who matches the art style that you want to capture or else you'll end up paying money for something that doesn't match your vision.