Hi - Great question and you've already received some great answers.
Here is a great article, "Don't hire a business coach who can't answer these 7 questions."
The article is writting by an E-Myth coach which I am not certified by... I just happen to like his questions.
Certification, in my opinion, isn't relevant either (and I'm certified). What is relevant? Results.
Google is your friend. If you've short listed a few coaches - google them. Don't be impressed by what the coach is saying, look for what others are saying about the coach... Linkedin endorsements are good... Recomendations are the best. No news is not good news in my opinion. If a coach is good, he/she will leave a trail of positive info.
Where to find a coach? The mall of course ;-) Ask people who you admire and look up to - Do you have a coach? Who did you use? Or... search Linkedin. Do you need a face-to-face coach or would web based coaching be okay (different delivery but just as effective with apps like Skype, GoTo Meeting etc.
What to watch for? If it sounds too good to be true... run. If they guarntee results... run. If they themself don't have a coach... run. Remember, you're interviewing them as much as they're interviewing you - are they asking thought provoking questions??
How much sshould you expect to pay? The better question is, how much are willing to invest (innn YOU). I personally would avoid any coach who charges an hourly rate... I've never met an "hourly rate" coach who makes a full time living and has the wealth and time you're looking for. Look for a program fee... and "program" means that you have access to your coach coach above and beyond your designated sessions with out being charged more.
As well, experience isn't as important as results. You could hire a coach with 10 years experience but can't inspire someone to get results. Or you can hire someone with 9 months experience but has a digital trail of results... make sense?
Lastly, where to find a coach... well, for starters... me. Google me and then give me a call at 403-874-7376. There is no fee for asking questions.
That said, you have 4 other coaches who've answered your question so far who have invested time in YOU. Start with them
Lastly, I beleive in sharing knowledge without expectation... give me a call.
All the best... and congrats for even asking the question.