Bug,
It's not the cost of obtaining patents that is the problem - although for a small company/individual the cost can be a problem. The real issue is defending them. All a patent does is give you the right to sue if somebody copies your invention...so what happens if a Multi-national corporation decides it likes joe-public's patent and is going to use it? Can joe-public really expect to take on a huge corporation in the courts? (Financially speaking.) They would just bleed you dry, wait for you to curl up and die and then carry on regardless.
My opinion is that you should just avoid letting them know how you did it! Keep you hard-earned knowledge to yourself! Or do it Dave's way and make it unpatentable!
Hope this helps
CRAN