There are numerous individuals, businesses and resorts currently offering these services. Unless you have something "unique, new and different" to offer, starting up a new business in any of these areas (diving / fishing / tour guides, etc) would be duplication of services.

Tour guides have very specific requirements (I believe they have already been covered here), but it is very difficult for a non-citizen to obtain. Others can assist with rates of pay, but I would venture a guess of BZ $10 /hour (US $5) for an experienced and licensed tour guide (independent contractor).

And, IMO, even if you were able to secure the proper licensing, doing so could be viewed as a threat.