I think having a professional editing is completely necessary if you're going to self-publish. Funny I should see this thread. I just posted a post on my
website. I talk about how much an editor cost me ($2000) and the estimates I got from other editors. It was worth every penny. I know I'll talk how I chose my editor at some point.
It's a lot of money but just start saving it. It's not like you have to pay all at once. 1/3 now and the rest about a month or two later.