Rock Crusher Canyon RV Park is a very nice place and convenient to most everything around Homasassa & Crystal River (nice area). It's maybe 20 miles from Cedar Key itslef, but an easy drive up the highway. There are several other parks around the area, depending on just what you prefer for amenities.
Suwannee River Hideaway is also a favorite place of ours, but not as close to the area attractions (except for Manatee Springs). Wonderful for relaxed camping, though, and the owners are splendid hosts.