Water Jet cutting has quickly become the most popular method of cutting due to its diverse applications. I know of a local sign company that has all of their "die-cut" signs cut by a waterjet cutter. I, also, know of a machine shop that has parts cut using waterjets. However, the machines do come at a cost. I would suggest contacting a water jet manufacturer and getting a quote for your application so you can judge for yourself if you would be able to make a healthy living using one of the machines. Of course, it will also depend on how much competition there is in your area.

WaterJet manufacturer: http://semyx.com/