I'm just starting out, but I already know that I'll handle the marketing myself, mostly due to my limited budget. I've taken a couple of free Udemy marketing courses that I think will help me along. Hopefully.
I just do it myself Paul. I'm small potatoes and I'm not looking to get rich off of this at this point. I consider a good marketing campaign as simply posting my work in places where good number of people will see it.
I would hope that there are agents out there who would only charge a fee if they are successful in getting your video published, similar to a literary agent. Well, in an ideal world, that would be the case.
There are many factors to consider before hiring a professional, and cost is one of them. I the beginning, you may have to handle the marketing yourself, either as a way to learn or to understand the market.