my small bussiness has been sent a certified letter from an attorney from CA, concerning Intellectual property infringment.

Almost always, there is a demand for a payment of fees in a cease and desist letter. You have no legal obligation to pay those fees because there is no judgment against you or an agreement with them under which you have to pay them. They would have to bring a lawsuit against you to get a judgment that would force you to pay them. The cost to draft and file a copyright infringement complaint would almost certainly equal or exceed $750.00, so the likelihood of them taking this action is perhaps not high. However, that is not to say they won't do that. If they were to file a copyright infringement lawsuit, they have to prove that you are liable for copyright infringement. A discussion of that issue and how it may play out in an infringement litigation is something you would need to discuss with an attorney who can see the details of what was on your website and what was complained of, and also find out whether the complaining party had registered the copyright before the material was on your website.