You could do another option that works for a few of the parks in Wisconsin.
You pay to park, but you get your tag a little differently. You put it into a disc golf box, get your parking permit and then that money is guaranteed to go back to the disc golf course. If you have to pay the ranger station, you simply say "I am here to play disc golf." Instead of getting the standard green parking ticket, you get a special orange one, then if your vehicle is not in the disc golf area, you still show you have paid, but it again accounts for the disc golf dollars that is a new revenue stream.
You could also ask for a discounted park permit, but I tend to agree with cooper, $40 for a year of golf if I lived in the area would be a no-brainer. You may be able to sell some to the club, or take money the year in advance and see if you could get the park to offer a $25/disc golf permit......just sayin......