Wow. Our budget is $750/month.
We just spent a week on the beach in the Keys: $270.00. Yes, it was a state park, but we had a site on the beach. No sewer hookup, but we easily made due without one.
We alternate between Passport America campgrounds and public campgrounds. For the next few days, our Passport America campground is charging us $15/day. That makes up for the $38/day we paid in the Keys. There are public parks that have sewer (we stayed at a couple last week in Florida) but they don't have weekly or monthly rates. But, in high demand areas, such as Florida in the winter, the prices are very hard to beat. I think the most we have paid for a campground is around $45 per night.
An easy way to lower costs is to learn to conserve water. W/E sites are always cheaper than W/E/S sites. There are also many more available. Many people use a tote to empty their tanks so they can stay at state beach campgrounds (Florida, South Carolina, MD, NC). It would drive me crazy to only stay at full hookup sites. There are some amazing campground in state and federal parks that offer no hook ups at all.