Legal Question in Intellectual Property in California

Your question is like asking how much it costs to build a house. It all depends on what's involved. How complicated is the patent and the product? How similar is the allegedly infringing product? Is this something that would require a lot of expert analysis to help determine (your lawyer may not be skilled in the particular area of science necessary to evaluate the case himself or herself)? Is the patent valid? How many products are involved? How much work on the analysis of similarity have you already done?

The short answer is that you will need to ask a lawyer about the specific patent and the specific products involved. A good lawyer can then give you an estimate as to your specific situation. You may be able to have the lawyer put in a certain amount of work and then give you a preliminary opinion. Just keep in mind that this likely to be an expensive project, running into the thousands of dollars.