It looks like KOA is about $40 a night, and at that point you might want to look at budget hotels, which might not be much more.
You might want to look at Fort Tuthill, which offers camping for military families for just $9. There is also a county park with a similar name. Not sure about showers on either of them though. You mentioned nothing being "as close" as the KOA. Is there a specific reason you need to stay in town?