Hi Simon, I partially agree with clikbill, because unlike neighboring countries, Sri Lanka seems to be a lot easier to work in, if you follow the rules and work with the Government.
There are many ways of doing what you want to do, one is to do it by yourself by getting the necessary permissions/licenses/approvals etc., the other is to get some local hired help, the third would be to join someone who has already gone through the legal procedures of setting up a business for foreigners, and could easily add another small venture and perhaps partner to the company, making it an overnight job for you to get a permanent residence visa and clearing all the hurdles to get started right away!
If you opt for option 3, you would need to provide many more details, such as what do you need to import, because we do have a healthy fibreglass industry here specifically in boat building, and many of those materials are available locally.
Infrastructure costs close to nothing here (compared to Australia), you could get a land for perhaps $10,000 and build a basic factory on it for another $10-15,000 only! (Or lease an existing house to use as a factory for only around $100-$150 per month). This is, of-course, in the suburbs, not in the main cities.
Let me know if you require further help or clarification!
Best of luck!
Sam.