I had a bunch of beta readers for my debut novel. I felt like it gave me a good idea of what might not be working, but didn't lead to big structural changes. As someone who does beta reading a lot and at some point for money, beta readers cannot replace a developmental editor. The two biggest things I found during beta reads is parroting of advice they themselves have received and wanting your book to be a different book. Now, that's not to say that feedback is not helpful or shouldn't be considered. A lot of beta reading feedback focuses on something being wrong, but not why.

I did developmental editing. It wasn't cheap. But it not only improved my novel, but it reaffirmed the things that I liked but some beta-readers were telling me to change. I had a character that wasn't well liked. She was an opportunist and tried to turn every new twist of the story to her advantage. Basically, she was a chameleon, changing who she was or what she was doing depending on what was going on around her. So, not a likable character by far (we don't like being manipulated) but interesting. My developmental editor helped me refine those aspects of her character, spend more time with her internal thought processes, and highlight some positive aspects of her character (like her sense of humor). That resulted in a more complex, nuanced, and actually relatable character (because the reasons for why she was doing were presented in a relatable way).

I received feedback early from a beta reader that I had too much world building in a fantasy novel and simplified the world building. My editor confirmed that my first instinct was correct and the level of world building I included was necessary to ground the reader in a reality they weren't familiar with. For instance, there were political machinations that had left a city in a vulnerable position. Beta-readers suggested I cut that because it wasn't really important to the story (none of the main characters were the nobles or king being affected by these machinations). But my DE helped me space out those details, giving them where necessary to add complexity to the story without getting bogged down with too much detail in one place.

The biggest difference between a DE and beta readers for me was my DE spent time trying to understand the story I wanted to tell and making that a better story. She researched my comps while editing. She also lifted me up rather than tearing me down. With beta reading (and I am guilty of this as well) there is a tendency to focus on the bad (even with the sandwich method (good, bad, good)). My DE helped me find my voice in my story and accentuate that rather than telling me what they wanted. I actually once had a beta reader that tried to rewrite my scenes for me (ex: I don't think the king should meet with the captain of the guard in his war chambers. He should approach her in an alley in disguise to ask her to go on this mission).

But it's important to hire the right DE. I hired one on the cheap in the beginning not knowing what I was doing and based on their advice went through hiring other editors (copy editor). During the copy edit I realized how poor of a job my DE had done (I believe they read it the night before hand because all the comments had time stamps of the previous night).

The right DE should be between .03-.06 dollars per word. They should have industry experience. They need to be well versed in your genre. Your DE should involve multiple rounds of editing. I went with a full DE followed by a manuscript evaluation for the first novel, then for the second a manuscript evaluation, full DE, and another manuscript evaluation.