There are a lot of different types of documents which need to undergo process serving in order for them to become legally valid. "Process Serving" is the actual act of presenting someone with a legal document like a summons, a writ, or a subpoena. You've probably encountered a process serving before if you've ever had someone present you with a legal document like a subpoena. This is an essential part of the court process, and while it can be slightly different from state to state, depending on the particular laws of where you live, you need to understand that this service is always going to be a part of many different kinds of legal proceedings.
Process serving can cost different amounts depending on where you live and what company you go with. There are companies which are dedicated to this service only, and there are also companies which might have several different areas of business that they are involved in, such as those which might do this service but also be involved in the San Francisco courier service. It's important to find a company which does good work but offers affordable rates. You shouldn't expect to pay more than $100 for process serving, and the cheapest you might be able to find may be around $45. It would be reasonable to expect that most prices would fall somewhere in between those two figures.
The reason that this process is so important is that in certain areas for a document to be actually legal it is going to have to be physically received by the person who is named in the document. This is in many cases an important part of the procedure, and is one reason why it can be very important to take the time to search around to find a company or business who is competent and good at their job, as they will have to find the person named in the document and present it to them in person in order for it to be legally enforceable.
If you're in the legal industry and need to find a good company which offers such a service, you should ask around amongst your colleagues in order to find out what local companies they have used. If you find a company which can offer you reliable service at a reasonable rate then you've got a company that you can probably continue to do business with for many years into the future.