I don't care if you're planning on publishing the traditional route or self-publishing, you need a good editor for both venues.
You might ask why, if you're publishing traditionally, you should hire an editor for your manuscript if the big publishing house will already rake its editorial fingers through your piece.
You're hunting for an agent, aren't you? Or are you lucky enough to know of a few publishing houses that will look at unrepresented manuscripts? You'll want to put your best book forward and show them as close to a clean copy as you can create.
If you're self-publishing, hiring an editor should really be a no-brainer. You also want to put your best book forward and not alienate your readers with syntax errors, typos, and major grammatical no-nos.
Not only do I write for my own series, but I'm also a freelance editor for The Dragon's Rocketship LLC and run a Gig through Fiverr.com. Do you need an affordable editor? Hire me.