Editing is like eyebrow maintenance. Some things you just shouldn't do yourself.
Now, before you get all up in arms and argue about pricing, or freelancers who don't do their job well, or any of the many arguments I've heard by butthurt indie writers who take that observation personally (man oh man, we writers are a sensitive bunch!), allow me to elaborate.
You can, indeed, edit your own work just as you can, indeed, tweeze your own eyebrows. It just takes a lot more time, work, and tools than letting a professional with a better perspective do it. If you really can't afford an editor, then you'll need a good mirror with satisfactory magnification, a good pair of tweezers, fantastic lighting, time, patience, pain tolerance, and a steady hand.
Funny as it sounds, you need those exact same things if you're going to edit your own work. Because everyone knows a first draft is crap. And no, you are not a beautiful and unique snowflake who manages to crank out the only existing first draft that is a work of art. It's crap. Go through it slowly, line by line. Pull out what doesn't work; yank it out by the roots. It hurts, yes. So what? Grow tougher. Expose it in the full light of day to many different pairs of eyeballs. Qualified eyeballs.
And no, your mother, spouse, or besties don't count. Unless your besties happen to be editors, university English Professors, or Nobel laureates in literature. Then it's okay.
There are plenty of editors out there who are quite affordable, and very qualified. Do your due dilligence there, too. Ask for references, and follow up with them. Ask what their payment policies are, if your work is the only one they'd work on or if there are others they edit co-currently. Do they have a blog or email newsletter? Subscribe to it. Friend them on Facebook, or follow on Twitter. Read their reviews on Goodreads and Amazon. In short, get to know them. Are they kind of a Grammar Nazi? Good! When it comes to making your manuscript the best it can be, a Grammar Nazi is your best friend.
I promise, you'll thank me for it later. And your manuscript --and your eyebrows-- will definitely look better, too.