As pedalpete mentioned, most of the time you'll want to do the bulk of the prority research yourself before you start costing lawyer and/or patent agent* time.

As pedalpete mentioned, most of the time you'll want to do the bulk of the prority research yourself before you start costing lawyer and/or patent agent* time. We submitted a few patent applications during my master's research project, that the university eventually bailed out on due to the industrial partner pulling out. The patent agents basically pulled a list of a few hundred (might have been a few thousand, there were many duplicates though) patents we had to go through and make sure they weren't prior art. We mainly used google patents. We reduced that list to less than 10 patents, which we then we through in detail with the agents, them explaining to us the subtleties of the law and patent specific language (words on patents don't always mean what you think they mean) and us explaining the technical aspects of our invention and how it's different. Overall though, I came out of the whole process feeling like the utility of patents for the independent inventor is very limited. Not to mention the initial time and cost to apply for a patent, think about the eventual cost if you need to actually defend it in court, ie, make actual use of the patent. Is protecting your invention worth this?