I recommend you don't spend money on editing services. You have (I'm guessing) TONS of secondary essays because you have applied broadly. Spending all that money to polish your content will not = interview. Go to your writing center on campus (or a community college nearby) and sit there all day while the tutors roam around the room. Repeat until you feel like you have gotten your message across.
If you are happy with a casual look over your essay, there are a few kind hearted members on SDN that are willing to take a look at secondaries. Check the sticky at the top of the Pre-DO page.
But heck, if you got the cash money, make it rain on those (shady) editing services online. Check craigslist even.