How about Career Coaching based in higher education? See "working for us" page of Careers Group for one example. Pay's okay and I think they value various sector experience more than qualifications.
Is there a particular age range of person that you would particularly enjoy coaching? Or people facing particular challenges?
Genius Within is perhaps another organisation you might like to look at for ideas. Quite education/specific learning difficulties related some of their work is I believe. May spark an idea of interest.
I agree that credibility is very important but that also comes from coaching technique. Yes as a business coach or business mentor you need to have a background in business, but other types of coaching I don't think necessarily require experience of having worked in a particular field.
Would slightly disagree with pp who says that qualifications aren't important..I believe that coaching skills need to be learned over time and quite formally in order to be able to practise safely and effectively. Not always the case but increasingly though I understand from coaching friends that corporate type organisations are requiring specific coaching qualifications before they contract a coach. I think it also makes coaching much more rewarding when you learn more about the theories and techniques, gain feedback from more experienced coaches and peers about how to motivate and support change rather than just relying on your own occupational experience.
I work as a careers coach with clients with mental health needs. Pay is approx 35K and I find it is extremely rewarding (been doing it about 8 years and have a masters in career coaching) Incredible variety of clients who are working at all levels from entry level to burnt out high flying exec. or with clients who may be looking for jobs in a variety of sectors and need coaching/advice on how to retrain. I find my job fascinating as it draws upon so many theoretical fields including educational psychology, occupational psychology, sociology etc etc etc!
For more info on Career Coaching qualifications you could look at the Careers Development website. For other types of coaching qualifications check out ICF or ILM
Good luck. Coaching is a very rewarding job. (I know less about mentoring). Agree self-employment can be difficult but if you find a niche not necessarily impossible.
Be really interesting to hear more from other types of coaches/mentors.
NB there are loads of initiatives these days that require volunteer mentors and coaches if you want to try it out and build experience. CIPD runs a few initiatives I believe with young people.