If you want to save money and need only the basics, try looking for "CL" sites (Certified Location). These are generally very small campsites, with basic water supply, dumping points, and sometimes electrical hookups, but without the clubhouses, swimming pools, shops, and other fancier facilities of the large sites. They are generally limited to just a few caravans (travel trailers) or tents at a time.
You should be able to find more information about CL sites on the link that Tam posted.