It will give you a good idea of the kind of organization with which you're dealing. Get of list of URLs the vendor has produced and check them out. Be sure to clarify what kind of services were provided for each site listed. You'll be able to determine how much time, care and attention your project will receive. Cost will vary greatly depending on what type of vendor you choose.
Some vendors charge by the hour, some by the project, and some by the page.
Some may charge one hourly rate for consulting and another for HTML markup. Be sure to ask detailed questions and for an explicit, written bid. Part-time employee and student work will vary based on the hours allotted. While this solution may be more economic at face value, consider the relative experience of these individuals against the size and scope of your project. Like many services, you get what you pay for.