Of course, there is no guarantee that an application will go through to become an issued patent. A complicated invention may end up costing several times that. In general, the biggest variable is how long it takes for the agent to understand the invention. The first step is always to see if it has been patented before. After an invention is either described publicly or sold, the inventor has only one year to file a patent application.
Inventors sometimes shoot themselves in the foot by waiting too long.
Sometimes that is true, but not always. If an invention is valuable enough to be stolen, there is a fair chance that it will be of interest to a second big league company as well, so you may find a partner with deep pockets. In the worst case, having a patent is a way to allow you to keep doing what you are doing with your invention. Having the patent yourself is a whole lot better than someone else having the patent on the same invention. Trade secrets are an alternative, if you are sure no one else will figure out how to do what you are doing for the economic life of the product.