State and national parks are almost always cheaper than private campgrounds. They do have that 14-day rule but you could either rotate out to a more expensive private campgrounds for a few days and return or, if available, go to another state/national park and rotate between them. Some have showers, some don't. I believe some also have a number of days you have to be out of the park before you can come back...I think it's 7 days but you'll really need to double-check that.

Preparing your own meals is obviously a key thing for saving funds.

Another option might be to try to get jobs in the service industry that caters to the tourism industry where you are. It may not pay as well as substituting or construction but, if those jobs aren't available, it could be a lot of fun. If you're there in the high-season, it might be fairly easy to find a job doing that.