"Good value" depends on what you are looking for. There are lots of ways to find campsites, some general in nature and others specific to certain style of camping. Yo will probably want to experiment a bit until you settle into what you like for your own style, so don't make any large or long term $$ commitments until you gain some experience.
There are some inexpensive discount clubs, e.g. Passport America & Good Sam. And lots of free listings online and free or cheap smart phone apps.