I think the only situation where it should be ok to work in something only for the money is if you're doing it for a temporary time and plan to change your situation soon, would still be hard to sustain and not sure if it's worth it, it'll vary from situation to situation
sometimes one can work a lot for, let's say, 5 years and then be set for decades.
Plus, a competition and a work is not the same thing, even if you get paid in the end. Art for work and art for competition have different reasons, if you work and earn a salary and your job is to create art then its fine, its one thing. But, if you are working a not making any profit at all and just end up doing art for hobby and want to test yourself with the results here with a competition? Thats sitll something for fun and not something serious.
After all you do not know how great or terrible it will be. Its not always the quality of the art, but the meaning of it. You could do something with amazing quality but with no soul in it, and could lose to someone who draws stickman but can make you feel something from it.