I have heard of consultants that charge up to 2K for this service. I don't believe in it. It strikes me as excessive and it has the potential to mislead the school (which is not ethical in my book nor is it to your child's advantage to trick your way into a place that is over their head).
But, I did get some good tips from one who gave a talk at our high school (which was free, because I suspect she gets clients that way

Her advice was to start by interviewing your child. Write down all of the topics/moments/experiences that they seem passionate about when they talk. You will find your focus in there somewhere. When you/the child picks that idea (use one that will allow her to showcase some of her positive traits/unique characteristics that make her someone a college would want in their community), then the child should OVERWRITE in response to the prompt--meaning that they should write two or three times what they need. THEN, have maybe two adults (one an english teacher? most high schools help with this) start editing it down. That way, it is the child's "voice" but someone more experienced can just polish it up, point out places where the organization goes off track, nominate passages for deletion, etc.
The goal, according to this consultant, is to get the admissions person to feel something about your child. If they have come across as an individual, the admissions staffer is more likely to fight for them at an admissions session. Last but not least, we have heard that the essay only carries so much weight: it can't salvage a child who is clearly unqualified to go somewhere, and is unlikely to sink a child who checks all of the school's boxes. They are important for that large, middle group, who will only get through if they have an advocate at the table.
Hope that helps!